A Valuable Technique for Industrial Parts

• What is pressure forming?
• Is pressure forming a new process?
• What is pressure forming capable of providing?
• Is the process faster that injection molding?
• Will it cost me a lot to change my design? 
• How does it compares to other processes?
• What can pressure forming do for me?

Pressure forming uses the vacuum forming process -evacuating air from the sealed space between the heated sheet and the mold, allowing atmospheric pressure (14.7 psi) to force the sheet to conform to the mold.- with the added step of applying 20-80 psi of compressed air to heated sheet, forcing it to conform to the mold surface.

This added step requires a supply of compressed air and additional sealing device on top of the sheet. Additional clamping force is used to prevent breaking the seal when applying high air pressure. The additional pressure results in superior surface finish and more accurate mold reproduction. 

Pressure forming has been around since the 1960's primary for thin-gauge sheet for packing applications, but it wasn't used much for industrial parts until the early 80's.

Pressure forming is proving to be a valuable technique for manufacturers of housings for computers, businesses machines, and other electrical equipment. It is enabling them to get parts into the market quickly that have the look of injection molding, without the lead times or tooling expense. It can provide the structural integrity, aesthetics and design flexibility usually found only in injection molded parts.

More specifically, pressure forming is capable of providing:

• sharp edges
• under cuts and reverse drafts
• tight corner radii
• multiple-textured surfaces
• better control of wall thickness for structural integrity
• embossed lettering 
• and other fine surface detail.

Tele-electronic equipment manufacturers found that pressure forming is a good alternative to injection or structural foam molding when they needed small volumes of parts very quickly. It is not designed to compete with injection or structural foam molding in high-volume or complex design requirements. However, it does offer some very real advantages where tooling costs, short lead times or low volumes production are factors.

Product life cycles have changed in the last 4-5 years. While they  used to be on the order of 3 years, it is now more likely to be 8 -12 months, particularly for telecommunications equipment. The whole project, from design to production, rarely takes more than 12-18 months.

Another factor to consider is that design changes can be made to the mold and secondary fixtures for a fraction of the cost of the same changes in other techniques.

A general rule thumb when considering pressure forming is the larger the part or the smaller the volume, the greater the advantage for pressure forming. Here are the specifics:

• Lead Times: -- Prototyping and tooling for pressure forming generally takes 8 - 12 weeks vs. 18-26 weeks with the traditional injection molding. Depending on the part, some thermoformers can complete tooling in 6-8 weeks. Structural foam and RIM tools do not take as long to build as injection molds, but do take longer than pressure forming tooling. Depending on the undercuts and texturing required, vacuum forming tool can generally be slightly faster than pressure forming tools.

• Tooling costs -- Injection molds are generally higher than pressure forming tools, and the larger the part, the greater the difference between the two processes. For example, the tooling cost for pressure formed 4 x 6 in. valve cover is $1,850, vs. $12,000 for injection molds. With a 25 x 35 in. part, however, the difference between tooling cost is much greater - $8,000 vs. $70,000. Pressure forming tooling can be as low as 10% of the cost of injection molding tools, as injection molding requires matched tooling.

  The most important factor to keep in mind when making a cost comparison is finding the break point. In the case, of a 4 x 6 in. valve cover, the break point for pressure forming vs. injection molding is 4000 parts, while for the 25 x 35 in. part, the volume break point would be much higher.

  Sharp undercuts (90°) that provide hidden fastening devices or insure good mating surfaces can be designed into the part. Undercuts are very difficult with conventional vacuuming forming. Sharp corners or areas that required 0° or negative draft angels are possible on parts having smooth surfaces.

• Processing -- Much of the expertise in pressure forming is in the tool itself. Cast or machined or fabricated aluminum tooling is recommended. Epoxy has not been very successful, as room temperature needs to be controlled, and it has to be able to withstand the pressures. With undercut, fabricated tools are recommended; it is difficult to cast tools with undercuts. Fabrication also enables part designs to be changed. 

Besides tooling, there are few other factors to take into consideration:

Thermoforming machines with mechanical driven platens are desirable in order to withstand the additional pressure., which ranges from 20 to 80 psi, though it is not usually over 50 psi. Upper and lower platen are required, with heavy duty frames.

Plug assist is required in pressure forming the same parts that would need it if vacuum formed. Pressure forming generally requires thicker sheet than a vacuum forming, due to the process ability  to produce greater detail, sharp corners and the need to duplicate "the heft" of injection and structural foam molding.

Pressure forming is providing to be a valuable technique for manufacturers of housing for computers, business machines and other electrical equipment. It is enabling them to get parts to market quickly that have the look of injection molding, without the lead times or tooling expenses. It can provide the structural integrity, aesthetics and design flexibility usually found only in injection molded parts.

Cost Savings

• Save up to 80% of tooling expenses

• Cost effective production runs

• Ideal for short runs

• Reduce Inventory on schedule parts

Shorter Lead Times

• Tooling turn around to 6 weeks

• Production can begin in 8 weeks

Advantages of Pressure Forming

• Parts are attractive and durable

• Sharp Definition

• Consistent part dimensions

Engineering Advantages

• High-tech product look

• Tight corner radii

• Zero or negative draft angles, undercuts

• Wide range of mold textures and painting options

• Economical design conversion from other processes

• Consistent repeatability on production runs