The material class of fiber-reinforced materials has shown a substantial growth in the
last couple of years in the high-performance range like aerospace and motor sports,
as well as in mechanical and plant engineering, in the automobile industry and in
the commercial vehicles market. Important reasons for this growth are the advantageous
properties of these materials, which are seen in the high specific strength and
stiffness as well as a fatigue and corrosion behavior. Fiber-reinforced materials are
used as lightweight materials in various shapes for different applications.
When processing fiber-reinforced materials, apart from the group of in situ polymerized
thermoplastics, thermoplastic and thermoset processing have to be differentiated.
The essential distinction is the temperature control and the resulting
viscosity of the processing masses, which is very low or water-like in a thermoset
material and significantly higher or honey-like in a thermoplastic material.
The process temperature determines significantly the choice of the plastic mold material,
and the material property viscosity determines the sealing system of the molds.
Other division characteristics are the fiber length, fiber orientation, and the fiber
amount (fiber volume ratio of the product to be produced). The fiber structure
determines (through its compression behavior) the necessary resistance or stiffness
of the mold and also influences the material choice for the mold construction.
The different thermal expansion coefficient between mold and component has to
be taken into consideration when choosing the material. Fiber-reinforced materials
show a very different behavior depending on fiber direction and type of fiber
(glass or carbon fiber). Finally, specific restrictions for processing procedure and
the processing variation have to be considered in mold construction.
Plastic injection molding is a very cost-effective way to produce high-quality parts. Even so, there are a number of things you can do to save even more money on a project without sacrificing anything in the finished product.
Use designs that minimize materials. Features like ribs and gussets can make a part stronger while using less material. Even a small reduction multiplied by the many parts in a production run and potentially many production runs can add up to big savings.
Ensure adequate draft. In injection molding, as in all manufacturing processes, time is money. Parts that have the appropriate amount of draft allow faster ejection from the mold and save precious seconds.
Consider mold longevity in your design. The more frequently you have to replace your molds, the higher your overall cost of producing parts. Consider the features of a mold that allow it to hold up over time as you design your parts.
Use materials that meet—but don’t grossly exceed—your needs. While it’s critical that your raw materials meet your requirements, using resins that go far above them or have qualities unnecessary to your project, is simply wasting money. Don’t skimp, but don’t splurge. Explain to your material provider what you are trying to accomplish but also let them know that you want to do so economically.
Produce as many parts at a time as possible. Spreading setup costs over a large number of parts results in a lower cost-per-piece.
Minimize secondary processes. Secondary processes like custom inserts, painting, etc. are necessary in some cases. In others, however, changes to design or materials can accomplish the same goals without the additional setup fees. The same is true for mechanisms. Many types of mechanisms, like living hinges for example, can be created in the molding process rather than after the fact.
Choose the right shop.Plastic injection molders tend to have specific areas of expertise. Finding one whose specialty meets your needs ensures that you won’t be paying more to have a molder modify its processes to accommodate your requirements.
Use the proper material to satisfy your demand ,not the highest.the material cost takes a very big part of injection molding expense,the proper plastic material decision would save you most.
The more money you can save on producing your plastic parts (without cutting corners, of course), the more competitively you can price your finished product. Use the tips above to give your company the edge.
Having become assured that the foregoing conditions have been fully met let us proceed with the train of thought. It is necessary to lay out a certain sum for plastic injection molds plant equipment and operating expenses. The amount needed will be governed entirely by the size of plastic injection molds plant required to produce the items previously determined. Of course, the major part of this capital investment will go into injection molding machine equipment, boiler, high and low pressure pumps, an accumulator and a compressed air system, but some of the smaller necessities such as piping, valves, finishing machines, furniture and fixtures, must not be omitted from the calculations.
If selfcontained injection molding machine are going to be used there will be no need for the machine auxiliary equipment. Whether the funds for procurement of this machinery shall be placed at $10,000 or $100, 000 is contingent also upon the size of plant to be built. An other factor which enters into the determination of this figure is the type of machinery purchased. Returning to the capital required, however, it should be kept in mind that the source of this money is of utmost importance.
All enterprises of whatever nature in business are founded on either money or credit and the terms of financing have a great deal to do with the fixed capital charges under which this enterprise must labor. It is essential then that any such terms be distinctly and thoroughly understood before any papers are signed. A misunderstanding in this direction may prove to be a hazard too difficult to overcome at a later date and very often failure may become obvious even before the project is far under way. Terms of financing should be such that provision is made for any exigencies that might arise during the course of the first few years.
It is a fairly simple matter to prognosticate certain conditions, but many times sufficient allowances are not made. An engineer when designing a bridge has to figure live and dead loads, stresses, and strains in every strut. After he has completed his calculations he then applies what is known as a “factor of safety”—which is actually nothing more than a ratio. He first theoretically calculates safe beam sizes and then multiplies by a certain constant to take into account the unknown hazards, such as possibly a record breaking snowfall or some other unusual happening.
In business, there are unfortunately a great many more hidden hazards than there are in the safe construction of a bridge, but after taking into account everything that can possibly happen it is always a sensible idea to apply a factor of safety of at least 2 to 1. This, of course, should not be interpreted too literally and does not mean that if $100,000 was decided upon as the amount necessary for fixed investment and operating expenses, the figure should be doubled. It does mean, however, that if fifty percent were set aside for operating expenses that an additional $50,000 would be adequate insurance for all contingencies.
So many enthusiastic enterprisers subconsciously deceive themselves and awaken only too suddenly (and usually too late), to find that they had been too optimistic at the outset. The application of a definite factor of safety should positively be made and will, in many instances, be the means of sustaining a business otherwise doomed to failure through lack of sufficient funds for continuance.
The following table gives the tolerances possible through broaching and the recommended design tolerances for minimizing cost when a broaching operation is specified:
Holes and Splines
Tolerances possible… Tolerances, low cost..
0.0002 in. 0.002
0.0005 in. 0.002
0.0002 in. 0.002
When two or more parts are broached simultaneously, high dimensional accuracy (0.0002 inch) between the parts can be depended upon.
Surfaces. A fine finish is produced since burnishing is part of the operation. Usually no further surfacing operations are necessary. The tool marks evidenced in broached holes are axial rather than radial as in drilled or reamed holes. This is an advantage in close-fitting reciprocating parts, where radial lines may be objectionable because the high spots tend to wear rapidly.
Materials Suited for Broaching. Steels, cast irons, bronzes, brasses， aluminum, and a broad range of other materials are successfully broached with proper broach design and setup conditions. The best range for broaching of steels lies between 25 and 35 Rockwell C hardness, although steels of higher or lower hardness have been broached successfully. Soft and nonuniform materials are subject to tearing when broached. On surfaces of high hardness, the first tooth of the broach should cut beneath the scale or surface material, thus assuring longer broach life.
Economical Quantity. Except when standard broaches may be employed, broaching is economical only for large-quantity production (over 2,500 parts). This is true because of the relative high cost of the broaching tool rather than because of the cost of setup. Broaching setups are simple except for fully automatic operations and can be made relatively quickly.
Broaching Tools. As mentioned, broaching tools are expensive and are usually made specially for a given job. The broaching tool is made from a tough, wear-resistant alloy usually containing about 5 per cent tungsten and 5 per cent chromium.
Broaching tools must be handled carefully in order to prevent nicks in the teeth which would cause scratches in the work.
Design Factors. In designing, the engineer should see to it that the amount of stock to be removed should always be less than 1 % inch. Good design allows between y32 and inch of stock to be removed from the stool mould steel. If less than inch is removed, a clean surface cannot be assured.
Since the broach must be able to make an unobstructed pass through or across the stool mould steel, it is not possible to broach blind holes.
The chip space between successive teeth on the broach must provide sufficient reservoir for the chip. This chip space will limit the axial length of the surface to be broached with a single broach.
Several surfaces can be broached simultaneously. When multiple surfaces on the same steel for stool mould making are broached, care must be exercised in designing the fixture to provide adequate strength to withstand the combined cutting tooth pressure. When gears or splines are to be cut, mechanical, hydraulic, or pneumatic indexing equipment is frequently provided.
Broaching provides high repetitive accuracy (applicable to production of large numbers of parts of close tolerances and fine finish) and close dimensional relationship of several surfaces broached simultaneously. Broaching is 15 to 25 times faster than other competitive machining methods. The process can be used to accurately produce internal and external surfaces that are difficult to machine by other methods.
The principle disadvantage of broaching is the high cost of special broaching tools. This cost usually does not permit the process to be used when production requirements are low. Then, too, it cannot be employed economically for the removal of large amounts of stock (more than Y> inch). Lastly, the process has application only on unobstructed surfaces permitting the pass of the broach through the plastics stool mould.
Broachings’ principle applications are for the production of almost any desired external or internal contour. This includes flat, round, and irregular external surfaces, round and square holes, splines, keyways, rifling, and gear teeth.
Oil Hardening Tool Steel for Auto Car Trim Mould Making
The oil hardening tool steels are probably used in plastics auto car door mould manufacture as extensively as are all of the other mold steels together. This includes carburizing steels, hobbing steels, water and air hardening steels.
Next to the air hardening steels, those which may be hardened by quenching in oil have the lowest distortion characteristics of all of the tool steels. The distortion of oil hardening tool steels upon heat treatment is less than the tolerance limits for some plastics mold applications, and this advantage, coupled with favorable machinability, accounts principally for their wide use. When the accuracy limits for finished mold parts are closer than the expected distortion, it is often possible to make allowances for distortion, and thus still hold the required accuracy with an oil hardening tool steel.
Hardness control, from extremely hard to fairly soft surfaces, is possible when oil hardening tool steels are used. Brightly polished surfaces, having good abrasion and crushing resistance, may be produced on car bumper mould cavity parts made of these steels. Guide pins, bushings, cams, cutting tools, and other mold parts which require high strength and hardness are usually made of oil hardening tool steels for best all around results.
The analyses of ten typical oil hardening steels which are used extensively for plastics molds are tabulated in Fig. below