How to build a one – off fiberglass part (the easy way)

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How to build a one – off fiberglass part (the easy way)

Here is described the way how I make fiberglass parts. You will not find it written like this in any other book or article. This method is simple and easy, it does not require any special or fancy tools, skills or materials, anybody who is capable enough to build an airplane should be able to follow it and make his own custom fiberglass components like cowlings and fairings.
The page is not the best it can be yet, so far the two projects described here were actually made a long time ago, back when I didn�t have a website, didn�t even have a computer and digital camera and I wasn�t trying to document the process and didn�t take the right pics. I have all of it now so from now on the future projects will be much better documented.

In order to be able to make that fiberglass part you have to construct a model of the part first. This model (called a “plug” in the fiberglass industry) must be made as accurate as possible with the thickness of the finished fiberglass lay up counted into the dimensions so any altering and filling of the laid up part is minimized. Since the plug is made out of foam, It�s far easier to shape then fiberglass or body filler so take a great care to do a good job on the shape of the plug and you will eliminate a lot of work later.
The foam used is the ordinary insulating kind from Home depot. It comes in different thickness and you will need to glue it up to get the needed block size. Don�t look at the necessity of gluing the foam sheets only as a nuisance, this glued up block has a very big advantage. When you shape your part, the glue lines serve as a guide to see how smooth your contours are and also the left to right symmetry can be seen easily without using templates. It works like magic.
To glue the foam sheets together use the “3M super 77 spray adhesive”. It�s the only glue I know of that will work on this. You can get it from Home Depot or hardware stores but don�t mix it up with the similar looking “3M high strength spray adhesive ” which will not work. Before gluing sand the surface of the foam with a large flat sanding block. This does two things, the surface of the foam has sort of harder skin like properties. This inconsistency in the material would cause raised ridges and wobbly surface when you�re sanding it to shape. The other reason is the surface to be glued must be perfectly flat. The contact adhesive is just that, it has absolutely no gap filling capability, it holds on contact so if there isn�t any the foam will be creeping apart and falling to pieces when you work on it.
Depending on the part the foam may be stacked horizontally, vertically, or a combination of the two. Sometimes if exact shape of the profile of the part at a certain plane (or a side) is known, a thin plywood template can be made and glued between the foam sheets into the exact position (or a side) and the foam is then simply shaped down to the template. In some cases a part of the plug can be cut out by a hot wire to a certain shape or an angle following straight edges or Formica templates of desired shape temporarily attached by nails.
The rough shaping of the foam is done by a large steak knife by shaving it off in thin slices. Keep it very sharp so it doesn�t tear the foam and be careful not to stab yourself. The surform file also works well for rough shaping and contouring. Sand to the final shape using proper sanding blocks, go to the Finishing a composite airplane page and read all about sanding , it all applies here the same.
You may have read in other books and articles directions how to finish the surface of a plug using plaster or epoxy fillers primers and lacquers to prevent sticking of the fiberglass part to the plug and enable the successful separation of the two. None of this finishing is necessary , all you need to do is apply the 2 inch plastic packaging tape neatly all over the foam plug and wax it. Epoxy resin does not stick to this plastic at all and the finished part will release with ease. The tape will bridge all the small nicks and smooth out the minor surface imperfections.

Fiberglass cloth to make the part can be purchased in many different weave styles which have different weight thickness and working characteristic but there are only several that are commonly used that I will describe here. Probably the most basic style is “7500” also commonly called boat and tooling cloth. This cloth weighs about 10oz./sq.yd, .14″ thickness, has plain fairly open weave which allows easy wetting out and fairly good contouring. The yarn in this cloth is twisted which gives it higher thickness for faster build up. The disadvantage of this cloth is that surface of the part is left very rough requiring more sanding and finishing work so its better not to use it as a last ply in the lay up.
Second common style is 7781, a little lighter and thinner then 7500 at about 9oz./sq.yd, .009″ thickness, this cloth has very tight weave so its harder to get the air bubbles out and it does not go well around compound curves. It�s a good choice for flat or single curved parts, the finished lay-up is left very smooth requiring only very little filling and finishing.
The third style is RA7725BID also known as Rutan cloth, about 10oz./sq.yd, .12″ thickness, this cloth has moderately tight crowfoot weave which enables it to go very well around compound curves but the disadvantage of that is that the fibers get easily disturbed and out of position and the edges tend to unravel and fall apart so it must be handled very carefully at all times.
The last one is 1522, this is very light weight and tight weave cloth 3.6oz./sq.yd, .0055″ thickness, good as the last ply on the lay-up to smooth out the surface.
Most common parts like cowlings, wingtips, fairings and moldings will require two to four plies using one, or a combination of, the first three types described above. The resin used is epoxy, I use Aeropoxy on almost all of my parts, but other epoxies can be used as well. I do not use and do not recommend the use of polyester resins.
The lay-up . Before you start the lay-up, precut all the cloth and stack it in reverse order so you have it ready and know which piece goes where. As you start the cutting, try to form the dry cloth onto the plug to determine what is the best yarn orientation that enables the cloth to stretch and form to the plug without creases, folds or cuts. Also see how the dimensions of the cloth change.
The lay-up technique depends on the size and the shape of the part. Sometime its better to position all of the cloth dry over the plug and then wet out all the plies at once, sometime its better to put it on one ply at a time. To wet out the cloth, a squeegee, a brush or a small paint roller can be used, one tool will work better then another depending on the size and the shape of the part.
Finishing of the part will depend on how good a job you made on the construction of the plug and how good finish you want. For a perfect finish you can follow the directions on Finishing a composite airplane page. If you have a fabric covered airplane some fiberglass parts can be finished with fabric as well.

منبع :

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بدنه دستگاه پزشکی (1)

ساخت بدنه یونیت پزشکی

ساخت بدنه یونیت پزشکی به روش ترمو فورمینگ با متریال پلاستیک ABS و کیفیت بسیار بالا

یکی از خدماتی که به طور تخصصی در گروه صنعتی آرشین انجام می گردد شامل طراحی از ابتدا تا تولید نهایی محصول و تحویل آن به مشتری می باشد.در این روش با بررسی مشخصات مورد نیاز محصول از مشتری ، نیاز ها ، نمونه های مشابه موجود و توقعات و قدرت سرمایه گذاری . محصول مورد نیاز از ابتدا طراحی شده و پس از تهیه نمونه سه بعدی کامپیوتری وارد پروسه ساخت و نمونه سازی می گردد.

در این مطلب با نحوه طراحی یک یونیت پزشکی آشنا می شوید. این دستگاه به عنوان کاور یکی از تجهیزات پزشکی مورد استفاده در اتاق عمل مورد استفاده قرار میگیرد.

جهت شروع پروسه تولید همانطور که در بالا گفته شد ابتدا بر اساس نیاز های کارفرما،محصول فوق به صورت اسکچ های دستی طراحی شده و پس از مشخص شدن فرم کلی،محصول مورد نظر در نرم افزار های سه بعدی مدل سازی می شود. در این پروسه از نرم افزار راینو استفاده شده است .این پروسه در بخش طراحی صنعتی شرکت انجام می گردد.

مدل سه بعدی محصول

مدل سه بعدی دستگاه

پس از تهیه فایل سه بعدی و تایید کارفرما، این فایل جهت پروسه قالب سازی و ریختگری آلومینیومی به واحد تولید ارسال می گردد.

در ادامه نمونه رندر کامپیوتری محصول را ملاحظه می نمایید :

رندر کامپیوتری محصول

رندر کامپیوتری محصول

تهیه فایل سه بعدی و رندر های کامپیوتری باعث می شود تا بتوان درک درستی از محصول نهایی به دست آورد و هرگونه ایراد یا تغییرات بر روی فایل کامپیوتری انجام شده و نیازی به دوباره کاری در بخش قالب سازی ایجاد نگردد.

پس از اتمام بخش طراحی ، قالب ها جهت تولید به واحد تراش سی ان سی ارسال شده و مدل اولیه قطعه به وسیله دستگاه تراش سی ان سی با دقت یک دهم میلیمتر تراشیده و ساخته می شود. در نهایت این قطعه به روش ترمو فورمینگ یا وکیوم و به وسیله ورق پلاستیک ای بی اس تولید می گردد. این ورق بسیار مستحکم و مقاوم به شرایط تخریب جوی می باشد. این متریال به خوبی رنگ پذیر بوده و کیفیت نهایی بسیار خوبی نیز خواهد داشت.

در ادامه تصویر محصول تولید شده را ملاحظه می نمایید :

بدنه دستگاه پزشکی (1)

بدنه تجهیزات پزشکی ساخته شده به روش ترمو فرمینگ یا وکیوم

بدنه دستگاه پزشکی (2)

متریال ساخت پلاستیک ABS و پوشش رنگ اپوکسی

از مزایای این روش به نسبت قطعات فایبرگلاس می توان به سرعت تولید بالا ، کیفیت سطح بیرون و داخل مناسب و یکسان ، ظاهر صنعتی و هزینه تولید مناسب تر اشاره نمود .


قسمت داخلی پوسته بدنه مانند قسمت بیرونی بسیار صاف و صنعتی بوده و مناسب کاور و کیس تجهیزات و دستگاه های حساس و دقیق می باشد.

گروه صنعتی آرشین توانایی طراحی و تولید تجهیزات ، قطعات و دستگاه های صنعتی را به روش فوق و با قیمت مناسب دارا می باشد.

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Fiberglass composites

From Wikipedia, the free encyclopedia
For the thermal insulation material sometimes called fiberglass, see glass wool. For the glass fiber itself, also sometimes called fiberglass, see glass fiber. For similar composite materials in which the reinforcement fiber is carbon fibers, see carbon-fiber-reinforced polymer.

Fiberglass (or fibreglass) is a type of fiber reinforced plastic where the reinforcement fiber is specifically glass fiber. The glass fiber may be randomly arranged, flattened into a sheet (called a chopped strand mat), or woven into a fabric. The plastic matrix may be a thermosetting plastic – most often epoxy, polyester resin – or vinylester, or a thermoplastic.

The glass fibers are made of various types of glass depending upon the fiberglass use. These glasses all contain silica or silicate, with varying amounts of oxides of calcium, magnesium, and sometimes boron. To be used in fiberglass, glass fibers have to be made with very low levels of defects.

Fiberglass is a strong lightweight material and is used for many products. Although it is not as strong and stiff as composites based on carbon fiber, it is less brittle, and its raw materials are much cheaper. Its bulk strength and weight are also better than many metals, and it can be more readily molded into complex shapes. Applications of fiberglass include aircraft, boats, automobiles, bath tubs and enclosures, swimming pools, hot tubs, septic tanks, water tanks, roofing, pipes, cladding, casts, surfboards, and external door skins.

Other common names for fiberglass are glass-reinforced plastic (GRP),[1] glass-fiber reinforced plastic (GFRP)[2] or GFK (from German: Glasfaserverstärkter Kunststoff). Because glass fiber itself is sometimes referred to as “fiberglass”, the composite is also called “fiberglass reinforced plastic.” This article will adopt the convention that “fiberglass” refers to the complete glass fiber reinforced composite material, rather than only to the glass fiber within it.


Glass fibers have been produced for centuries, but mass production of glass strands was discovered in 1932 when Games Slayter, a researcher at Owens-Illinois, accidentally directed a jet of compressed air at a stream of molten glass and produced fibers. A patent for this method of producing glass wool was first applied for in 1933.[3] Owens joined with the Corning company in 1935 and the method was adapted by Owens Corning to produce its patented “fibreglas” (one “s”) in 1936. Originally, fibreglas was a glass wool with fibers entrapping a great deal of gas, making it useful as an insulator, especially at high temperatures.

A suitable resin for combining the “fibreglass” with a plastic to produce a composite material was developed in 1936 by du Pont. The first ancestor of modern polyester resins is Cyanamid‘s resin of 1942. Peroxide curing systems were used by then.[4] With the combination of fiberglass and resin the gas content of the material was replaced by plastic. This reduced the insulation properties to values typical of the plastic, but now for the first time the composite showed great strength and promise as a structural and building material. Confusingly, many glass fiber composites continued to be called “fiberglass” (as a generic name) and the name was also used for the low-density glass wool product containing gas instead of plastic.

Ray Greene of Owens Corning is credited with producing the first composite boat in 1937, but did not proceed further at the time due to the brittle nature of the plastic used. In 1939 Russia was reported to have constructed a passenger boat of plastic materials, and the United States a fuselage and wings of an aircraft.[5] The first car to have a fiber-glass body was a 1946 prototype of the Stout Scarab, but the model did not enter production.


Unlike glass fibers used for insulation, for the final structure to be strong, the fiber’s surfaces must be almost entirely free of defects, as this permits the fibers to reach gigapascal tensile strengths. If a bulk piece of glass were defect-free, it would be equally as strong as glass fibers; however, it is generally impractical to produce and maintain bulk material in a defect-free state outside of laboratory conditions.


The process of manufacturing fiberglass is called pultrusion. The manufacturing process for glass fibers suitable for reinforcement uses large furnaces to gradually melt the silica sand, limestone, kaolin clay, fluorspar, colemanite, dolomite and other minerals to liquid form. It is then extruded through bushings, which are bundles of very small orifices (typically 5–25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass). These filaments are then sized (coated) with a chemical solution. The individual filaments are now bundled in large numbers to provide a roving. The diameter of the filaments, and the number of filaments in the roving, determine its weight, typically expressed in one of two measurement systems:

  • yield, or yards per pound (the number of yards of fiber in one pound of material; thus a smaller number means a heavier roving). Examples of standard yields are 225yield, 450yield, 675yield.
  • tex, or grams per km (how many grams 1 km of roving weighs, inverted from yield; thus a smaller number means a lighter roving). Examples of standard tex are 750tex, 1100tex, 2200tex.

These rovings are then either used directly in a composite application such as pultrusion, filament winding (pipe), gun roving (where an automated gun chops the glass into short lengths and drops it into a jet of resin, projected onto the surface of a mold), or in an intermediary step, to manufacture fabrics such as chopped strand mat (CSM) (made of randomly oriented small cut lengths of fiber all bonded together), woven fabrics, knit fabrics or uni-directional fabrics.

Chopped strand mat

Chopped strand mat or CSM is a form of reinforcement used in fiberglass. It consists of glass fibers laid randomly across each other and held together by a binder.

It is typically processed using the hand lay-up technique, where sheets of material are placed in a mold and brushed with resin. Because the binder dissolves in resin, the material easily conforms to different shapes when wetted out. After the resin cures, the hardened product can be taken from the mold and finished.

Using chopped strand mat gives a fiberglass with isotropic in-plane material properties


A coating or primer is applied to the roving to:

  • Help protect the glass filaments for processing and manipulation.
  • Ensure proper bonding to the resin matrix, thus allowing for transfer of shear loads from the glass fibers to the thermoset plastic. Without this bonding, the fibers can ‘slip’ in the matrix, causing localized failure.
  • Properties

    An individual structural glass fiber is both stiff and strong in tension and compression—that is, along its axis. Although it might be assumed that the fiber is weak in compression, it is actually only the long aspect ratio of the fiber which makes it seem so; i.e., because a typical fiber is long and narrow, it buckles easily.[7] On the other hand, the glass fiber is weak in shear—that is, across its axis. Therefore, if a collection of fibers can be arranged permanently in a preferred direction within a material, and if they can be prevented from buckling in compression, the material will be preferentially strong in that direction.

    Furthermore, by laying multiple layers of fiber on top of one another, with each layer oriented in various preferred directions, the material’s overall stiffness and strength can be efficiently controlled. In fiberglass, it is the plastic matrix which permanently constrains the structural glass fibers to directions chosen by the designer. With chopped strand mat, this directionality is essentially an entire two dimensional plane; with woven fabrics or unidirectional layers, directionality of stiffness and strength can be more precisely controlled within the plane.

    A fiberglass component is typically of a thin “shell” construction, sometimes filled on the inside with structural foam, as in the case of surfboards. The component may be of nearly arbitrary shape, limited only by the complexity and tolerances of the mold used for manufacturing the shell.

    The mechanical functionality of materials is heavily relied on the combined performances of the both resin (AKA matrix) and fibres. For example, in sever temperature condition (over 180 °C) resin component of the composite may lose its functionality partially because of bond deterioration of resin and fibre.[8] However, GFRPs can show still significant residual strength after experiencing high temperature (200 °C).[9]

    Types of glass fiber used

    Main article: Glass fiber

    Composition. The most common types of glass fiber used in fiberglass is E-glass, which is alumino-borosilicate glass with less than 1% w/w alkali oxides, mainly used for glass-reinforced plastics. Other types of glass used are A-glass (Alkali-lime glass with little or no boron oxide), E-CR-glass (Electrical/Chemical Resistance; alumino-lime silicate with less than 1% w/w alkali oxides, with high acid resistance), C-glass (alkali-lime glass with high boron oxide content, used for glass staple fibers and insulation), D-glass (borosilicate glass, named for its low Dielectric constant), R-glass (alumino silicate glass without MgO and CaO with high mechanical requirements as Reinforcement), and S-glass (alumino silicate glass without CaO but with high MgO content with high tensile strength).[10]

    Naming and use. Pure silica (silicon dioxide), when cooled as fused quartz into a glass with no true melting point, can be used as a glass fiber for fiberglass, but has the drawback that it must be worked at very high temperatures. In order to lower the necessary work temperature, other materials are introduced as “fluxing agents” (i.e., components to lower the melting point). Ordinary A-glass (“A” for “alkali-lime”) or soda lime glass, crushed and ready to be remelted, as so-called cullet glass, was the first type of glass used for fiberglass. E-glass (“E” because of initial Electrical application), is alkali free, and was the first glass formulation used for continuous filament formation. It now makes up most of the fiberglass production in the world, and also is the single largest consumer of boron minerals globally. It is susceptible to chloride ion attack and is a poor choice for marine applications. S-glass (“S” for “stiff”) is used when tensile strength (high modulus) is important, and is thus an important building and aircraft epoxy composite (it is called R-glass, “R” for “reinforcement” in Europe). C-glass (“C” for “chemical resistance”) and T-glass (“T” is for “thermal insulator”—a North American variant of C-glass) are resistant to chemical attack; both are often found in insulation-grades of blown fiberglass.[11]

    Table of some common fiberglass types

    Material Specific gravity Tensile strength MPa (ksi) Compressive strength MPa (ksi)
    Polyester resin (Not reinforced)[12] 1.28 55 (7.98) 140 (20.3)
    Polyester and Chopped Strand Mat Laminate 30% E-glass[12] 1.4 100 (14.5) 150 (21.8)
    Polyester and Woven Rovings Laminate 45% E-glass[12] 1.6 250 (36.3) 150 (21.8)
    Polyester and Satin Weave Cloth Laminate 55% E-glass[12] 1.7 300 (43.5) 250 (36.3)
    Polyester and Continuous Rovings Laminate 70% E-glass[12] 1.9 800 (116) 350 (50.8)
    E-Glass Epoxy composite[13] 1.99 1,770 (257)
    S-Glass Epoxy composite[13] 1.95 2,358 (342)


    Typical material appearance of a fiberglass Cryostat

    Fiberglass is an immensely versatile material due to its light weight, inherent strength, weather-resistant finish and variety of surface textures.

    The development of fiber-reinforced plastic for commercial use was extensively researched in the 1930s. It was of particular interest to the aviation industry. A means of mass production of glass strands was accidentally discovered in 1932 when a researcher at Owens-Illinois directed a jet of compressed air at a stream of molten glass and produced fibers. After Owens merged with the Corning company in 1935, Owens Corning adapted the method to produce its patented “Fiberglas” (one “s”). A suitable resin for combining the “Fiberglas” with a plastic was developed in 1936 by du Pont. The first ancestor of modern polyester resins is Cyanamid’s of 1942. Peroxide curing systems were used by then.

    During World War II, fiberglass was developed as a replacement for the molded plywood used in aircraft radomes (fiberglass being transparent to microwaves). Its first main civilian application was for the building of boats and sports car bodies, where it gained acceptance in the 1950s. Its use has broadened to the automotive and sport equipment sectors. In some aircraft production, fiberglass is now yielding to carbon fiber, which weighs less and is stronger by volume and weight.

    Advanced manufacturing techniques such as pre-pregs and fiber rovings extend fiberglass’s applications and the tensile strength possible with fiber-reinforced plastics.

    Fiberglass is also used in the telecommunications industry for shrouding antennas, due to its RF permeability and low signal attenuation properties. It may also be used to conceal other equipment where no signal permeability is required, such as equipment cabinets and steel support structures, due to the ease with which it can be molded and painted to blend with existing structures and surfaces. Other uses include sheet-form electrical insulators and structural components commonly found in power-industry products.

    Because of fiberglass’s light weight and durability, it is often used in protective equipment such as helmets. Many sports use fiberglass protective gear, such as goaltenders’ and catchers’ masks.

    Storage tanks

    Several large fiberglass tanks at an airport

    Storage tanks can be made of fiberglass with capacities up to about 300 tonnes. Smaller tanks can be made with chopped strand mat cast over a thermoplastic inner tank which acts as a preform during construction. Much more reliable tanks are made using woven mat or filament wound fiber, with the fiber orientation at right angles to the hoop stress imposed in the side wall by the contents. Such tanks tend to be used for chemical storage because the plastic liner (often polypropylene) is resistant to a wide range of corrosive chemicals. Fiberglass is also used for septic tanks.

    House building

    A fiberglass dome house in Davis, California

    Glass-reinforced plastics are also used to produce house building components such as roofing laminate, door surrounds, over-door canopies, window canopies and dormers, chimneys, coping systems, and heads with keystones and sills. The material’s reduced weight and easier handling, compared to wood or metal, allows faster installation. Mass-produced fiberglass brick-effect panels can be used in the construction of composite housing, and can include insulation to reduce heat loss.


    GRP and GRE pipe can be used in a variety of above- and below-ground systems, including those for:

    • Desalination
    • Water treatment
    • Water distribution networks
    • Chemical process plants
    • Firewater
    • Hot and Cold water
    • Drinking water
    • Wastewater/sewage, Municipal waste
    • Natural gas, LPG

    Construction methods

    Filament winding

    Filament winding is a fabrication technique mainly used for manufacturing open (cylinders) or closed end structures (pressure vessels or tanks). The process involves winding filaments under tension over a male mandrel. The mandrel rotates while a wind eye on a carriage moves horizontally, laying down fibers in the desired pattern. The most common filaments are carbon or glass fiber and are coated with synthetic resin as they are wound. Once the mandrel is completely covered to the desired thickness, the resin is cured, often the mandrel is placed in an oven to achieve this, though sometimes radiant heaters are used with the mandrel still turning in the machine. Once the resin has cured, the mandrel is removed, leaving the hollow final product. For some products such as gas bottles the ‘mandrel’ is a permanent part of the finished product forming a liner to prevent gas leakage or as a barrier to protect the composite from the fluid to be stored.

    Filament winding is well suited to automation, and there are many applications, such as pipe and small pressure vessel that are wound and cured without any human intervention. The controlled variables for winding are fiber type, resin content, wind angle, tow or bandwidth and thickness of the fiber bundle. The angle at which the fiber has an effect on the properties of the final product. A high angle “hoop” will provide circumferential or “burst” strength, while lower angle patterns (polar or helical) will provide greater longitudinal tensile strength.

    Products currently being produced using this technique range from pipes, golf clubs, Reverse Osmosis Membrane Housings, oars, bicycle forks, bicycle rims, power and transmission poles, pressure vessels to missile casings, aircraft fuselages and lamp posts and yacht masts.

    Fiberglass hand lay-up operation

    A release agent, usually in either wax or liquid form, is applied to the chosen mold to allow finished product to be cleanly removed from the mold. Resin—typically a 2-part polyester, vinyl or epoxy—is mixed with its hardener and applied to the surface. Sheets of fiberglass matting are laid into the mold, then more resin mixture is added using a brush or roller. The material must conform to the mold, and air must not be trapped between the fiberglass and the mold. Additional resin is applied and possibly additional sheets of fiberglass. Hand pressure, vacuum or rollers are used to be sure the resin saturates and fully wets all layers, and that any air pockets are removed. The work must be done quickly, before the resin starts to cure, unless high temperature resins are used which will not cure until the part is warmed in an oven.[14] In some cases, the work is covered with plastic sheets and vacuum is drawn on the work to remove air bubbles and press the fiberglass to the shape of the mold.[15]

    Fiberglass spray lay-up operation

    The fiberglass spray lay-up process is similar to the hand lay-up process, but differs in the application of the fiber and resin to the mold. Spray-up is an open-molding composites fabrication process where resin and reinforcements are sprayed onto a mold. The resin and glass may be applied separately or simultaneously “chopped” in a combined stream from a chopper gun. Workers roll out the spray-up to compact the laminate. Wood, foam or other core material may then be added, and a secondary spray-up layer imbeds the core between the laminates. The part is then cured, cooled and removed from the reusable mold.

    Pultrusion operation

    Diagram of the pultrusion process.

    Pultrusion is a manufacturing method used to make strong, lightweight composite materials. In pultrusion, material is pulled through forming machinery using either a hand-over-hand method or a continuous-roller method (as opposed to extrusion, where the material is pushed through dies). In fiberglass pultrusion, fibers (the glass material) are pulled from spools through a device that coats them with a resin. They are then typically heat-treated and cut to length. Fiberglass produced this way can be made in a variety of shapes and cross-sections, such as W or S cross-sections.


    One notable feature of fiberglass is that the resins used are subject to contraction during the curing process. For polyester this contraction is often 5–6%; for epoxy, about 2%. Because the fibers do not contract, this differential can create changes in the shape of the part during curing. Distortions can appear hours, days or weeks after the resin has set.

    While this distortion can be minimised by symmetric use of the fibers in the design, a certain amount of internal stress is created; and if it becomes too great, cracks form.

    Health problems

    In June 2011, the National Toxicology Program (NTP) removed from its Report on Carcinogens all biosoluble glass wool used in home and building insulation and for non-insulation products.[16] However, NTP considers fibrous glass dust to be “reasonably anticipated [as] a human carcinogen (Certain Glass Wool Fibers (Inhalable))”.[17] Similarly, California’s Office of Environmental Health Hazard Assessment (“OEHHA”) published a November, 2011 modification to its Proposition 65 listing to include only “Glass wool fibers (inhalable and biopersistent).”[18] The actions of U.S. NTP and California’s OEHHA mean that a cancer warning label for biosoluble fiber glass home and building insulation is no longer required under federal or California law. All fiberglass wools commonly used for thermal and acoustical insulation were reclassified by the International Agency for Research on Cancer (“IARC”) in October 2001 as Not Classifiable as to carcinogenicity to humans (Group 3).[19]

    People can be exposed to fiberglass in the workplace by breathing it in, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for fiberglass exposure in the workplace as 15 mg/m3 total and 5 mg/m3 in respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 3 fibers/cm3 (less than 3.5 micrometers in diameter and greater than 10 micrometers in length) as a time-weighted average over an 8-hour workday, and a 5 mg/m3 total limit.[20]

    The European Union and Germany classify synthetic vitreous fibers as possibly or probably carcinogenic, but fibers can be exempt from this classification if they pass specific tests. Evidence for these classifications is primarily from studies on experimental animals and mechanisms of carcinogenesis. The glass wool epidemiology studies have been reviewed by a panel of international experts convened by the IARC. These experts concluded: “Epidemiologic studies published during the 15 years since the previous IARC monographs review of these fibers in 1988 provide no evidence of increased risks of lung cancer or mesothelioma (cancer of the lining of the body cavities) from occupational exposures during the manufacture of these materials, and inadequate evidence overall of any cancer risk.”[19] Similar reviews of the epidemiology studies have been conducted by the Agency for Toxic Substances and Disease Registry (“ATSDR”),[21] the National Toxicology Program,[22] the National Academy of Sciences[23] and Harvard’s Medical and Public Health Schools[24] which reached the same conclusion as IARC that there is no evidence of increased risk from occupational exposure to glass wool fibers.

    Fiberglass will irritate the eyes, skin, and the respiratory system. Potential symptoms include irritation of eyes, skin, nose, throat, dyspnea (breathing difficulty); sore throat, hoarseness and cough.[17] Scientific evidence demonstrates that fiber glass is safe to manufacture, install and use when recommended work practices are followed to reduce temporary mechanical irritation.[25]

    While the resins are cured, styrene vapors are released. These are irritating to mucous membranes and respiratory tract. Therefore, the Hazardous Substances Ordinance in Germany dictates a maximum occupational exposure limit of 86 mg/m³. In certain concentrations may even occur a potentially explosive mixture. Further manufacture of GRP components (grinding, cutting, sawing) creates fine dusts and chips containing glass filaments, as well as tacky dust, in quantities substantial enough to affect people’s health and the functionality of machines and equipment. The installation of effective extraction and filtration equipment is required to ensure safety and efficiency.[26]

    Examples of fiberglass use

    Kayaks made of fiberglass

    See also


  • Mayer, Rayner M. (1993). Design with reinforced plastics. Springer. p. 7. ISBN 978-0-85072-294-9.
  • Nawy, Edward G. (2001). Fundamentals of high-performance concrete (2 ed.). John Wiley and Sons. p. 310. ISBN 978-0-471-38555-4.
  • US, “Method & Apparatus for Making Glass Wool”, published 11 Nov 1933, issued 11 Oct 1938
  • Marsh, George (8 Oct 2006). “50 years of reinforced plastic boats”. reinforcedplastics. Elsevier Ltd.
  • Notable Progress – the use of plastics, Evening Post, Wellington, New Zealand, Volume CXXVIII, Issue 31, 5 August 1939, Page 28
  • Hobart, Tasmania (27 May 1946). “Car of the future in plastics”. The Mercury. p. 16.
  • Gordon, J E (1991). The New Science of Strong Materials: Or Why You Don’t Fall Through the Floor. Penguin Books Limited. ISBN 978-0-14-192770-1.
  • Bank, Lawrence C. (2006). Composites for construction: structural design with FRP materials. John Wiley & Sons. ISBN 978-0-471-68126-7.
  • Russo, Salvatore; Ghadimi, Behzad; Lawania, Krishna; Rosano, Michele (December 2015). “Residual strength testing in pultruded FRP material under a variety of temperature cycles and values”. Composite Structures (ELSEVIER) 133: 458–475.
  • Fitzer, Erich; Kleinholz, Rudolf; Tiesler, Hartmut; et al. (15 April 2008). “Fibers, 5. Synthetic Inorganic”. Ullmann’s Encyclopedia of Industrial Chemistry. Ullmann’s Encyclopedia of Industrial Chemistry 2. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA. doi:10.1002/14356007.a11_001.pub2. ISBN 3527306730.
  • “Fiberglass”. Retrieved 28 Aug 2014.
  • “Guide to Glass Reinforced Plastics”. East Coast Fibreglass Supplies.
  • “Tube Properties”. Carbon Fiber Tube Shop.
  • Forbes Aird (1996). Fiberglass & Composite Materials: An Enthusiast’s Guide to High Performance Non-Metallic Materials for Automotive Racing and Marine Use. Penguin. pp. 86–. ISBN 978-1-55788-239-4.
  • James, Mike. “An Introduction to Vacuum Bagging Composites”.
  • “13th Report on Carcinogens”. National Toxicology Program. US Dept HHS. 2011. Retrieved 5 Feb 2013.
  • “Fibrous Glass Dust”. OSHA. U.S. Department of Labor.
  • 46-Z California Regulatory Notice Register, P.1878 (November 18, 2011).
  • “IARC Monographs Programme Re-evaluates Carcinogenic Risks from Airborne Man-Made Vitreous Fibres” (Press release). IARC. 24 Oct 2001.
  • “CDC – NIOSH Pocket Guide to Chemical Hazards – Fibrous glass dust”. Retrieved 2015-11-03.
  • Agency for Toxic Substances and Disease Registry (September 2004). “Toxicological Profile for Synthethic Vitreous Fibers” (PDF). US Dept HHS. pp. 5, 18.
  • Charles William Jameson, “Comments on the National Toxicology Program’s Actions In Removing Biosoluble Glass Wool Fibers From The Report On Carcinogens,” September 9, 2011.
  • NRC Subcommittee on Manufactured Vitreous Fibers. 2000. Review of the U.S. Navy’s Exposure Standard for Manufactured Vitreous Fibers. National Academy of Sciences, National Research Council, Washington, D.C.: National Academy Press.
  • Lee, I-Min; Hennekens, Charles H.; Trichopoulos, Dimitrios; Buring, Julie E. (June 1995). “Man-made vitreous fibers and risk of respiratory system cancer: a review of the epidemiologic evidence” (PDF). JOEM (LLW) 37 (6): 725–38. PMID 7670920.
  • “Insulation Facts #62 “Health and Safety Facts for Fiber Glass”, Pub. No. N040″ (PDF). North American Insulation Manufacturers Association (“NAIMA”). May 2012.
  • Türschmann, V.; Jakschik, C.; Rother, H.-J. (March 2011) White Paper, Topic: “Clean Air in the Manufacture of Glass Fibre Reinforced Plastic (GRP) Parts”. GRP Technique & Service
  • “Flexible Pavement Preservation Ch. 12 Interlayers” (PDF). Caltrans Division of Maintenance. January 27, 2009.
  • Staheli, Lynn T. (2006), Practice of Pediatric Orthopedics (2nd ed.), Lippincott Williams & Wilkins, p. 68, ISBN 9781582558189

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کاربرد کامپوزیت ها و فایبرگلاس در صنایع نظامی

radome fiberglass

کامپوزیت ها به دسته گسترده ای از مواد گفته می شود که معمولا ترکیبی از دو یا چند ماده با خواص متفاوت می باشد.هر ماده ویژگی خاصی دارد که جهت حصول به خواص فیزیکی و شیمیایی مورد نظر از ترکیب چند ماده استفاده می شود و به آن کامپوزیت اطلاق می شود.امروزه در بسياري از كاربردهاي فنی و مهندسي، به ترکیب خواص مواد نياز است و امكان استفاده از يك نوع ماده كه همه خواص مورد نظر را داشته باشد وجود ندارد . به عنوان مثال در صنايع هوافضا به موادي نياز است كه ضمن داشتن استحكام و سختی بالا، سبك باشند،مقاومت سايشي و مقاومت در برابر نور ماوراء بنفش خوبي داشته باشند و در دماهاي بالا سختی خود را از دست ندهند . از آنجا كه نمي توان ماده اي يافت كه همه خواص فوق را دارا باشد، بايد به دنبال روشي براي تركيب خواص مواد بود . اين راه حل همان مواد كامپوزيت است . كامپوزيت ماده اي چند جزئي است كه خواص آن از هركدام از اجزا بيشتر است، ضمن آنكه اجزا و ارکان مختلف كارايي يكديگر را بهبود مي بخشند.امروزه در حدود 17 درصد از سهم صنایع کامپوزیت در دنیا مربوط به صنایع هوافضا می باشد.کامپوزیت های رایج و پرکاربرد در صنایع هوافضا را می توان ترکیبی از الیاف گلاس یا شیشه ، الیاف کولار و الیاف کربن دانست و رزین های پر کاربردی که معمولا در ترکیب با این الیاف استفاده می شوند را می توان رزین های پلی استر ، ونیل استر و اپوکسی نامید که هر یک از این رزین ها خود به تنهایی دارای شاخه ها و انواع مختلفی بوده که توضیح آن در این مقاله نمی گنجد.از کاربردهای کامپوزیت ها به خصوص فایبرگلاس در صنایع نظامی را می توان در مواردی همچون پوشش رادار و کاور تجهیزات دریافت و ارسال سیگنال ، پوشش پوسته و بدنه انواع موشک ، جلیقه های ضد گلوله و کلاهخود سرباز ، پوشش های بدنه خودروهای نظامی ، بدنه بالگرد و هواپیما و بسیاری موارد استفاده دیگر نام برد که جز شاخه های بسیار تخصصی در صنعت کامپوزیت بوده و نیازمند دانش و تجربه بالا جهت ساخت آنها می باشد.از ویژگی های بسیار مهم کامپوزیت ها و فایبرگلاس که باعث شده است در صنایع نظامی بسیار مورد توجه قرار گیرد را می توان به وزن بسیار پایین در قیاس با سایر مواد مورد استفاده ، قابلیت عبور امواج جهت سهولت ارتباط دستگاه های رادیویی داخل تجهیزات نظامی مانند ارتباط موشک کامپوزیتی با کنترلر پرتاب ، رادارگریزی و عدم جذب امواج ، مقاومت در برابر خوردگی و عوامل شیمیایی را نام برد.گروه صنعتی آرشین افتخار طراحی و ساخت تجهیزات نظامی کامپوزیت را دارا بوده و همچنین امکان طراحی سه بعدی و تحلیل و آنالیز قطعات طراحی شده پیش از تولید در نرم افزار آباکوس وجود دارد.

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کامپوزیت چیست ؟

کامپوزیت چیست ؟

کلمات و واژه هایی مانند فایبر‌گلاس یا کامپوزیت برای شما نیز احتمالا آشنا و با آنها  مواجه شده‌اید. این مواد امروزه کاربردهای بسیار گستردهای در صنایع مختلف پیدا کرده‌اند. برای شروع بهتر است بدانیم که فایبرگلاس نوعی بسیار متداول از کامپوزیت است. حال باید دانست کامپوزیت چیست؟

رشد بسیار سریع و  فزاینده تکنولوژی در سال‌های اخیر باعث شد تا  موادی که در دسترس بشر بود برای پوشاندن جامه حقیقت بر رویاهای مدرن و ابزار های امروزی کافی نباشد و از این رو تلاش برای رسیدن به مواد جدید آغاز شد؛ مثلا در بیشتر کاربردهای مهندسی، اغلب به تلفیق خواص مواد نیاز داریم. موادی که ضمن داشتن استحکام بالا، سبک باشند، مقاومت سایشی و آنتی یو وی خوبی داشته باشند و سایر مواردی که بر اساس هر نوع استفاده مشخص می شود.

اما از آنجا که نمی‌توان ماده‌ای یافت که همه خواص مورد نظر را دارا باشد، باید به دنبال چاره‌ای دیگر بود: ساخت و استفاده از کامپوزیت‌ها.

سفر به فضا با شاتل‌های کامپوزیتی!

اگر مواد مهندسی را به سه دسته اصلی فلز، پلیمر و سرامیک طبقه‌بندی کنیم، کامپوزیت دسته چهارمی است که در واقع ترکیبی از 3 دسته دیگر است. موادی چند جزئی که خواص آنها در مجموع از هرکدام از اجزاء بهتر است. ضمن آنکه اجزای مختلف، کارایی یکدیگر را بهبود می‌بخشند.

استفاده از این مواد البته ایده جدیدی نیست. چینی‌ها و مصریان قدیم از جمله تمدن‌های باستانی بوده‌اند که برای اولین بار از مخلوط کاه‌گل و شن برای بناسازی استفاده کرده‌اند تا استحکام گل افزایش پیدا کند.

مصریان با چسباندن لایه‌های نازک چوب و پارچه به یکدیگر و با استفاده از طناب، قایق‌های خود را در برابر متورم شدن دراثر نفوذ آب تقویت می‌کرده‌اند.

اما استفاده از کامپوزیت‌های پیشرفته، از حدود نیمه دوم قرن بیستم آغاز شد.

چند نوع کامپوزیت داریم؟

وقتی در مورد انواع کامپوزیت صحبت می‌کنیم، منظورمان کامپوزیت‌های مهندسی است و نه کامپوزیت‌های طبیعی مانند استخوان‌های بدن.

کامپوزیت شامل یک فاز زمینه (ماتریکس) و یک یا چند فاز تقویت‌کننده (پرکننده یا فیلر) است. البته ترکیب مواد در کامپوزیت یک ترکیب فیزیکی و ماکروسکوپی است؛ یعنی اجزای تشکیل‌دهنده یک کامپوزیت با هم به صورت شیمیایی ترکیب نمی‌شوند به طوری که اجزای تشکیل دهنده ماهیت شیمیایی و طبیعی خود را کاملا حفظ می کنند و سطح مشترک مشخصی بین اجزا وجود دارد.

کامپوزیت‌های مهندسی را می‌توان از نظر فاز زمینه به 3 دسته CMC (کامپوزیت‌های با زمینهٔ سرامیکی)، PMC (کامپوزیت‌های با زمینه پلیمری) و MMC (کامپوزیت‌های با زمینه فلزی) تقسیم‌بندی کرد.

اما از نظر فاز تقویت‌کننده کامپوزیت‌ها به 2 دسته کامپوزیت‌های تقویت‌شده با فیبر (FRC) و کامپوزیت‌های تقویت شده توسط ذرات (PRC) دسته‌بندی می‌شوند.

به عنوان مثال فایبرگلاس که یکی از پرکاربردترین کامپوزیت‌هاست، یک کامپوزیت با زمینه پلیمری است که توسط فیبرهای شیشه تقویت شده‌است. سیمان و بتن هم نمونه‌هایی از یک کامپوزیت سرامیکی هستند.

کامپوزیت چه مزایایی دارد؟

مهم‌ترین مزیت مواد کامپوزیتی آن است که با توجه به نیازهایی که داریم، می‌توانیم خواص آنها را کنترل کنیم. به طور کلی مواد کامپوزیتی دارای مزایای زیر هستند:

• نسبت به وزن خود مقاومت مکانیکی بالایی دارند.

• مقاومت در برابر خوردگی آن‌ها بالاست.

• نسبت به فلزات خصوصیات مکانیکی بهتری دارند.

• به عنوان یک عایق حرارتی خواص خوبی دارند.

مجموعه این خصوصیات است که باعث کاربردهای گسترده کامپوزیت‌ها در صنایع نوین می‌شود. در ساخت بدنه جنگنده‌های رادارگریز از کامپوزیت‌ها استفاده می‌شود. همچنین در ساخت قطعات هواپیما و پره نیروگاه بادی و پره هلیکوپتر از کامپوزیت‌ها استفاده می‌شود. به‌طور کلی مواد کامپوزیتی به دلیل جرم بسیار کم و مقاومت بالا نسبت به فلزات، در صنعت هوا و فضا کاربرد وسیعی دارند.

خواص کامپوزیت‌ها به عوامل مختلفی از قبیل نوع مواد تشکیل دهنده و ترکیب درصد آن‌ها، شکل و آرایش تقویت‌کننده و اتصال ماتریکس و تقویت‌کننده به یکدیگر بستگی دارد.

کامپوزیت قالب فایبرگلاس فایبرگلاس قالب مدل سازی قالب رادوم قالب بتن قالب کامپوزیت

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پروژه ساخت قالب فایبرگلاس جهت ساخت نمونه مبلمان شهری بتنی

مبلمان شهری یکی از عناصر بسیار مهم در طراحی فضاهای شهری است که شامل عناصر گسترده و بسیار متنوعی از انواع تجهیزات روشنایی،راه بندها ، نشیمن ، ایستگاه اتوبوس،جدول ، سطل زباله ، گلجای و موارد بسیار دیگر می باشد.طراحی مناسب و دوستار کاربر باعث ایجاد رابطه مناسب فضای شهری با انسان ها شده و در نهایت باعث ایجاد آرامش ، علاقه و شکوفایی شهروندان در بستر جامعه خواهد شد.در پایان سال نود و چهار شمسی به مانند سال گذشته سازمان زیباسازی شهرداری تهران دومین دوره مسابقه دایره خلاق را با موضوع طراحی ست مبلمان شهری با در نظر گرفتن هویت فرهنگی منطقه بازار برگزار نمود .در نهایت پس از بررسی 350 اثر ارسالی 15 طرح به بخش ساخت راه یافت که در ادامی یکی از نمونه های ساخته شده در گروه صنعتی آرشین را ملاحضه می فرمایید.متریال ساخت طرح زیر بتن می باشد. جهت ساخت نشیمن به دلیل نیاز به استحکام بالاتر از بتن گلاسه استفاده شده است و پایه آن بجای سیمان معمولی رزین های صنعتی می باشد. بتن گلاسه در قیاس با بتن معمولی بسیار مقاومت بیشتری داشته و در عین حال هزینه مواد اولیه آن نیز بسیار بیشتر می باشد. طرح ایستاده گلجای از بتن مسلح تهیه شده است. جهت بتن ریزی نمونه های زیر به دلیل وزن بالا نیاز به قالب های بسیار مستحکم وجود داشت که به دلیل پیچیدگی فرم های موجود از دستگاه فرز سی ان سی و قالب فایبرگلاس استفاده شد.گلجای ایستاده در تصویر دارای وزن 1.3 تن می باشد و قالب فایبرگلاس به گونه ای طراحی شده است که تحمل وزن بتن ریزی را داشته باشد.جهت نمای بهتر از مواد افزودنی خاص جهت تهیه بتن دودی رنگ بجای رنگ روشن عادی بتن استفاده شده است.بتن یکی از مواد بسیار مقاوم در ساخت مبلمان شهری بوده و در برابر عوامل جوی ، آتش سوزی و عوامل تخریبی وندالیسم بسیار مقاوم بوده و می تواند به خوبی برای سالیان طولانی ظاهر و کارایی خود را حفظ نماید .گروه صنعتی آرشین توانایی ساخت انواع قالب های خاص بتنی از جنس فایبرگلاس جهت بتن ریزی نمای ساختمان ، مبلمان شهری و موارد مشابه را دارا می باشد .


قالب فایبرگلاس بتن مبلمان شهری بتنی کامپوزیت فایبرگلاس

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ساخت ماکت حجمی سنجاب از جنس فایبرگلاس

ماکت زیر یک کاراکتر سنجاب به سفارش شرکت غذایی سنجابک می باشد.این ماکت به ارتفاع 3 متر از جنس فایبرگلاس و در مدت زمان بسیار کوتاه یک هفته ساخته شده است.متریال فایبرگلاس در صورت انتخاب دقیق مواد مورد استفاده و کاربرد افزودنی های شیمیایی مناسب در پروسه تولید ، کیفیت بسیار بالایی در اجرای کاراکتر تبلیغاتی خواهد داشت.متریال فایبرگلاس در ساخت ماکت های حجمی و تبلیغاتی بسیار پرکاربرد بوده و ضمن داشتن وزن پایین و قابلیت جابجایی مناسب،عمر بسیار بالایی داشته و در برابر عوامل جوی مخرب مانند باران و اشعه خورشید نیز بسیار مقاوم است.ماکت های حجمی فایبرگلاس با استفاده از رنگ آمیزی براق و شارپ باعث جلب توجه بسیار مناسبی می شود و مانند یک بیلبورد چند وجهی در سطح شهر عمل می کند و بیننده از هر نمایی با مشاهده آن جذب و کنجکاو خواهد شد.عمر ماکت های فایبرگلاس در مقایسه با بیلبورد های پارچه ای یا بنر بسیار بالاتر بوده و به دلیل هزینه ساخت مناسب امروزه مورد توجه بسیاری از صنایع و تولید کنندگان قرار گرفته است. این ماکت پس از ساخت به مدت تقریبی ده روز در سطح شهر و تحت یک کمپین تبلیغاتی در معابر پر تردد شهر تهران به همراه اسکورت دو خودروی مرسدس بنز گردانده شد .گروه صنعتی آرشین آمادگی ساخت انواع ماکت و حجم های تبلیغاتی در ابعاد بزرگ را دارا بوده و با وجود متخصصین تحصیلکرده در این زمینه آماده ارائه مشاوره و ساخت در این زمینه می باشد.

Sanjab (2)

Sanjab (1)

Sanjab (3)

ساخت ماکت ماکت سازی ماکت فایبرگلاس بیلبورد تبلیغاتی ساخت ماکت حجمی ماکت سه بعدی ماکت تبلیغاتی حجم تبلیغاتی ساخت قطعات فایبرگلاس خدمات ساخت قطعات فایبرگلاس

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ویژگی های کامپوزیت

فایبرگلاس یکی از کامپوزیت هایی است که ترکیبی از یک رزین ترموست و الیاف مصنوعی می باشد.در پروسه ساخت قطعات کامپوزیتی می توان از انواع رزین های مختلف که رایج ترین آنها رزین پلی استر و رزین اپوکسی می باشد استفاده نمود.این رزین های به صورت مایع بوده و در ترکیب با الیاف مصنوعی و پس از قرار گرفتن در قالب سخت شده و فرم نهایی محصول را ایجاد خواهند نمود.الیاف مورد استفاده در کامپوزیت ها نیز بسیار متنوع و رایج ترین آنها را می توان الیاف شیشه ، الیاف کربن و الیاف کولار نام برد.مقاوت الیاف کولار به کشش بسیار بالا بوده و در کلاه خود و زره های نظامی از آن استفاده می شود.معمولا در قطعات خاص از ترکیب الیاف ذکر شده استفاده می شود تا ترکیبی از خواص کل الیاف باعث بدست آمدن کیفیت نهایی و مقاوت فیزیکی بسیار بالا شود. در حال حاضر الیاف شیشه رایج ترین مورد استفاده در صنعت را داشته و باعث استحکام بسیار خوب قطعات رایج در صنعت می شود.الیاف شیشه در ابعاد ، بافت و ضخامت های متنوع عرضه شده و مهندسین محاسب بر اساس تنش های وارده بر قطعه نوع و جهت لایه ها را تعیین نموده و میزان ترکیب رزین و الیاف را مشخص می نمایند تا ضمن حفظ حداکثر استحکام،میزان مواد مصرفی و وزن قطعات بالا نرود.