Simulation spots trouble before it starts.* Blow molding has been one of the slowest processing sectors to adopt simulation software Simulation software is based on the process of imitating a real phenomenon with a set of mathematical formulas. It is, essentially, a program that allows the user to observe an operation through simulation without actually running the program. as a design and troubleshooting tool. While injection molding injection molding
A manufacturing process for forming objects, as of plastic or metal, by heating the molding material to a fluid state and injecting it into a mold. and some extrusion processes have exploited the benefits of simulation for well over 20 years, blow molders still appear to be a little "computer-shy." In fact, even thermoformers appear to have embraced simulation faster than blow molders.
The areas of plastics processing Plastics processing
Those methods used to convert plastics materials in the form of pellets, granules, powders, sheets, fluids, or preforms into formed shapes or parts. that adopted simulation first were ones that had the most to lose if the product or process failed. The automotive industry The automotive industry is the industry involved in the design, development, manufacture, marketing, and sale of motor vehicles. In 2006, more than 69 million motor vehicles, including cars and commercial vehicles were produced worldwide. placed very high demands on injection molders, making the molds expensive and forcing companies to improve efficiency and reduce delivery times. Simulation was welcomed as a form of' insurance against the costs and delays inflicted by an unworkable tool design. Suppliers of large extrusion dies also realized that it made a great deal of sense to gain more confidence in the performance of their designs before cutting any steel.
In these cases, the cost of failure could easily be over $100,000. This forced injection molders and extruders to stop wasteful trial-and-error design methods and adopt simulation as a standard procedure. However, there was a perception in blow molding that the cost of failure is relatively low. Mold costs are typically lower and blow molded products are generally used in less demanding applications. This may be the main reason blow molders did not place more emphasis on simulation.
Times have changed
Over the last few years every industry has placed a stronger emphasis on cost reduction and efficiency. Most companies now realize that the true costs of product development include more than mold rework--wasted material, lost production time, and late delivery, which is probably the most important and most difficult to value. Combine this realization with the influx of inexperienced in·ex·pe·ri·ence
1. Lack of experience.
2. Lack of the knowledge gained from experience.
in designers replacing an aging work force and you have conditions where simulation can provide a benefit.
Computer simulation allows the user to test various hypotheses in the comfort and safety of the office without the high cost, lost production time, and risk of equipment damage associated with physical experimentation on the shop floor. The benefits of simulation toward problem solving problem solving
Process involved in finding a solution to a problem. Many animals routinely solve problems of locomotion, food finding, and shelter through trial and error. (or better yet, "virtual troubleshooting") are demonstrated below with a few examples using the commercially available B-SIM extrusion blow molding simulation software package.
n. 1. (Glassworking) An intermediate stage or shape of a glass object which is produced in more than one stage. profiling
The first example shows the benefit of simulation in determining parison size and shape for a relatively simple oval bottle. Figure 1 predicts the thickness variation in the bottle based on different initial parison diameters and thickness profiles. It is clear from the color contour contour or contour line, line on a topographic map connecting points of equal elevation above or below mean sea level. It is thus a kind of isopleth, or line of equal quantity. map that a profiled parison with different thicknesses around its circumference is more successful in achieving uniform bottle thickness than merely increasing the diameter of the parison.
[FIGURE 1 OMITTED]
Figure 2 illustrates that point another way. The simulation software produced a graph of the thickness values that would be predicted to occur around the circumference of the bottle for each of the starting conditions shown in Fig. 1. The results show that the 38-mm-diam. parison resulted in very thin walls at the ends of the oval bottle shape. The 50-mm-diam. parison made the thin areas a little thicker but at the expense of extra (wasted) material on the flat sides of the bottle. The 50-mm parison with a profiled wall thickness from 1 to 2 mm resulted in a much more uniform overall wall thickness and a 25% reduction in overall material usage.
[FIGURE 2 OMITTED]
For more complex shapes, axial axial /ax·i·al/ (ak´se-al) of or pertaining to the axis of a structure or part.
1. Relating to or characterized by an axis; axile.
2. profiling (extrusion-direction thickness adjustment) is another wall-thickness optimization tool that can be simulated.
Poor design remedied
Figure 3 shows a series of steps in the simulation of blowing a fluid tank or jerry can jer·ry can also jer·ri·can
A flat-sided can for storing or transporting liquids, especially gasoline, having a capacity of 5 gallons (19 liters).
[From Jerry. . To the inexperienced molder mold·er
v. mold·ered, mold·er·ing, mold·ers
To crumble to dust; disintegrate.
To cause to crumble. See Synonyms at decay. , the design may appear simple enough to go ahead and build a mold. But simulation can point out some potential problems with the design.
[FIGURE 3 OMITTED]
The simulation shows that the material has some difficulty forming the top of the tank in the handle area resulting in a "web" or "wrinkle Wrinkle
A feature of a new product or security intended to entice a buyer. " and a very thin wall--possibly a blow-out. This would require some design change to the tank, and of course, the mold would have to be reworked if the problem were not avoided by simulation.
An experienced blow molder might be able to alert the designer to a potential problem, but the question is how much confidence the designer or molder should have that any design modification would adequately correct the problem. First, simulation can be used to help convince the part or mold designer that the design should be modified. And second, the simulation can help determine how much of a modification must be made.
Finally, it should be emphasized that the simulations presented here can be performed in a few hours using relatively inexpensive PC hardware.
John Perdikoulias is vice president of Compuplast, a multinational company that specializes in polymer processing simulation software and services. He has over 18 years of experience in design and process optimization Process optimization is the practice of making changes or adjustments to a process, to get results.
Optimization is the use of specific techniques to determine the most cost effective and efficient solution to a problem or design for a process. in plastics. He can be reached at (905) 814-8923, email@example.com
By John Perdikoulias
Compuplast North America North America, third largest continent (1990 est. pop. 365,000,000), c.9,400,000 sq mi (24,346,000 sq km), the northern of the two continents of the Western Hemisphere.