Materials & Applications
Material selection for mold and trim press processes are paramount to the success of car manufacturers. Aesthetics, formability, finish, weight, colour, touch and feel are all important. Mold and trim produced parts are often required to house and hide wires and electronics, making it easy for assembly, maintenance, and possible replacement.
Engineered plastics, with low material density, durability, and dimensional stability, have proven to be a superior choice for automotive mold and trim parts. Acrylonitrile-butadiene-styrene (ABS), polycarbonates (PC), ABS/PC alloys, polypropylene (PP), modified polyphenylene ether (PPE), and styrene-maleic anhydride (SMA), are just some of the examples of modern plastic polymers that are regularly used.
These types of plastics allow for complicated designs and complex shapes to be formed. A single piece that integrates many features can be manufactured resulting in seamless and aesthetically pleasing designs and finishes. There can be significant cost savings for manufacturers as colour can be added directly to resins, finishing techniques can give the plastics the look and feel of complementary fabrics, graining, and high/low gloss paint.
Plastic polymer materials are well suited for flexible and versatile designs that result in stylish aesthetically pleasing, scratch resistant, durable interior automobile components. Considerations for vibration, noise, UV resistance, climate, off gassing, post life recycling of material are additional challenges car manufacturers face when designing and choosing materials for their products.
Twin sheet molding: This process involves both methods of vacuum forming and pressure forming of two sheets simultaneously within a temperature-controlled platen press. Each sheet is first heated and vacuum formed to an individual mold, that are mounted to the top and bottom platens of the press. The platens are brought together quickly to maintain the temperatures and the two formed sheets are bonded together under high pressure. The resulting piece is a single hollow product that requires no additional bonding.
Compression molding: A common manufacturing process that uses thermosets, thermoplastics, elastomers, and rubber materials to produce parts varying in size, thickness and complexity. The materials used are generally pre heated and formed by pressing into a mold cavity and applying a controlled pressure. Common automotive parts produced with compression molding include; hoods, fenders, spoilers, and smaller more intricate parts.
Plastic thermoforming and vacuum: Materials such as vinyl and soft touch plastics that are widely used in finished car interiors can be produced via vacuum and plastic thermoforming. A plastic sheet is placed above a mold and heated, and a press will force a mold towards the sheet as it forms and creates a seal. Vacuum is then applied to ensure the material takes proper shape of the mold. The press is configured such that curing takes place under a temperature-controlled environment, and the plastic part is then separated from the mold resulting in a high-quality finished piece. Because of factors such as material and heat application, much lower forming pressures are required with this process. Both tooling costs and requirements for high tonnage presses are reduced, making it a viable process for parts for the automotive industry as it can be used of varying sizes and production quantities.
A number of pieces and parts for automobiles can be produced with vacuum and plastic thermoforming including bumpers, truck beds, and floor mats. Various colours, finishes, and even environmental considerations for the materials and final parts are possible making it an important process for car manufacturers as they strive to appeal to consumers and varying individual tastes.
Establishing Process Parameters
The process for mold and trim is always specific to the individual parts being created and material being used. Factors such as heat distribution, temperature control, and ejection methods, are just some of the variables in addition to the typical press process parameters.
The bed of a mold and trim press must be able to accommodate the footprint of the largest expected toolset. The orientation of the part is important for overall forming, but will also determine the overall requirements for bed dimensions. Wide access to the bed from all four sides of the press is advantageous for both automated and manual handling of materials and parts.
Tonnages and Speeds
Trimming of parts requires appropriate tonnages for how the finished part will be cut based on the specific geometry, material, and tooling.
A hydraulic mold and trim press can be controlled to open and close as quickly as needed. But with mold and trim parts, the speed and cycle times for production are often driven by the necessary pressure, and heating and cooling requirements to form the individual parts and material. The complexity of the part, surface finish, and handling are often limiting factors on how fast the parts can be produced rather than the press speed itself.
Stroke and Daylight
Enough daylight must be available between the fully retracted tool faces to allow removal of the finished part from the press. In practice, this translates to daylight that is approximately triple the press stroke. If a press will be used to produce more than one part, stroke and daylight should accommodate the largest expected tooling. Additional clearances may be required to accommodate in die cooling, in die heating, robot or feeder access, and quick-change tooling.
Hydraulic Mold & Trim Presses
Some of the options that a hydraulic mold and trim press can be fitted with include:
- Heated platens
- Tilting tables
- 180-degree rotating platens
- Rack & pinion leveling systems
- Rolling bolsters / shuttles
- Vacuum systems
- Auxiliary circuits for core / eject functions
- Remote diagnostics package
With an endless number of different options and packages that can be customized, hydraulic mold and trim presses remain a flexible and long-lasting option for automotive manufacturers. Automobile manufacturers usually offer a number of trim levels with each car, and their designs can undergo refresh programs as quickly as 1-2 years. It is important that hydraulic mold and trim presses have the ability to keep up with this constantly changing environment.
- Some of the major advantages of using mold and trim hydraulic presses for automotive interior parts include:
- Efficiency – fast and repeatable production
- Complex part design
- Flexibility in material, colour, and finishes of parts
- Lightweight and strong parts
- Reduced material waste
- Precision and accuracy of parts
- Fig 1: M&T_P-F1, Silvestro, Brian, Road and Track, These Are the 20 Best New Car Interiors, October 9, 2019
- Fig 2: M&T_P-F2, Basics of Thermoforming (https://kydex.com/technical-resources/thermoforming-processes)
- Fig 3: M&T_P-F3, A 1000 Heated Platen Press, Macrodyne
- Fig 4: M&T_P-F4, A 250 Ton Mold and Trim Press, Macrodyne
- Fig 5: M&T_P-F5, Two 150 Ton Mold and Trim Press Machines, Macrodyne