Applications of Rapid Prototyping for Automotive Industry

Interior and exterior parts are crucial to the appearance and functionality of an automobile, and the vast majority of these components are manufactured using the injection molding process. The reasons are that injection molding offers excellent consistency in part formation, can mold relatively complex shapes, has high production efficiency, and yields relatively inexpensive parts. Its main drawback is the high cost of the official production molds.

Therefore, to ensure that the actual parts achieve the designed visual effects, meet ergonomic requirements, and satisfy assembly structure needs, it is necessary to manufacture rapid prototyping samples for vehicle assembly verification before developing the official molds. Using RP samples to verify design schemes can significantly accelerate time-to-market, reduce development costs, and shorten the product development cycle.

Currently, the mainstream methods for manufacturing rapid prototyping samples for automotive interior and exterior parts in the domestic and international automotive industries are mainly divided into four categories: CNC machining, 3D printing, soft tooling, and reaction injection molding. Among these, 3D printing is a method that has undergone rapid development in recent years. Below is an introduction to the principles and application scenarios of these methods.

CNC machining generally refers to using Computer Numerical Control (CNC) equipment to directly machine block plastic materials, such as Acrylonitrile Butadiene Styrene (ABS) or Nylon, into the required shapes according to the design scheme. If the dimension is less than 300 mm and the structure is simple, it is directly machined in one piece. If the structural shape is irregular or the dimension exceeds 300mm, the part is usually divided into several small blocks, machined separately, and then spliced and assembled to finally obtain a part that meets the design dimensions.

This is the earliest method of manufacturing rapid prototyping samples. It features a relatively short processing cycle and lower procurement costs. It is mainly used for small and medium-sized parts with relatively simple structures and low demand quantities, such as pillars, center consoles, and door trim panels.

Due to styling needs, automotive parts are usually irregularly circular or square. When dimensions exceed 300 mm or the shape is irregular, using a single solid block of plastic multiplies the cost. Therefore, in actual manufacturing, the part is split based on its structural features, rough-machined to approximate the desired shapes, and then glued together with special adhesives to form the overall contour. Finally, it is precision-machined as a whole. This effectively reduces material waste and lowers part costs.

Obvious bonding marks can be seen on the back of the part where the blocks are joined, and the bonded areas have poor strength and are prone to cracking.

3D Printing technology is based on digital model files, utilizing bondable materials such as powdered metal or plastic to construct objects layer by layer. Its application fields are very broad, and the manufacturing of RP samples is one of its important directions.

Samples produced via 3D printing have shorter cycles and can achieve complex, irregular structures. The overall dimensional accuracy can be adjusted according to actual needs. Generally, 3D printing can manufacture the same range of parts as CNC machining, suitable for rapid prototyping of pillars, center consoles, and door trim panels.

Common Materials:

ABS-like Plastic: Low unit price and good molding performance, suitable for structural parts with low strength requirements.

Nylon: Good strength and better heat resistance than ABS-like plastics, but relatively expensive.

Nylon + Glass Fiber: An enhanced version of standard nylon, suitable for parts requiring higher strength.

Photosensitive Resin (UV Resin): Composed mainly of polymer monomers and prepolymers containing photoinitiators. Under specific ultraviolet wavelengths (250~300 nm), it instantly triggers a polymerization reaction to solidify. It features fast curing, high precision, excellent surface finish, high mechanical strength (comparable to ABS-like), low odor, strong versatility, and long shelf life.

Soft tooling primarily refers to silicone molds and Fiberglass Reinforced Plastic (FRP) Molds.

Silicone Mold

Typically, the designed part is first obtained via CNC machining or 3D printing, and then this master part is used to create the mold. This process has a short cycle and low cost, utilizing methods like urethane casting, pressure casting, and low-pressure perfusion for production.

It is suitable for small-batch production under 100 pieces, requiring high strength and dimensional accuracy, yielding strength close to conventional ABS. The silicone rubber used is a two-component liquid, categorized into condensation cure and addition cure. It is used for small/medium interior trim parts like door panels, pillars, and scuff plates.

FRP Mold

 FRP is a composite material using glass fiber and its products like cloth, tape, mat, yarn as reinforcement and synthetic resin as the matrix.

It is similar to silicone casting, FRP molds are usually used for medium-to-large decorative parts with simple structures, such as headliners and carpets. Suitable for compression molding, blister molding, and foam molding that meet the needs of 100~1000 sets.

Reaction injection molding involves mixing two or more low-viscosity liquids in a specific ratio under certain pressure and temperature conditions, and immediately injecting them into a closed mold where they undergo a chemical reaction to form a plastic product.

Simple equipment, mold scalability for large parts, high strength and surface quality of molded parts, and dimensional stability. Part thickness can range from 6 to 25 mm. The disadvantage is a higher unit price and the inability to mold complex structures.

Mold materials can be low-cost epoxy resin or cast aluminum, drastically reducing costs compared to official molds. Suitable for small batch trials of 100~200 sets/month. Molds are typically directly CNC machined with an approximate 12-day cycle, plus 3 days for assembly and testing. RIM parts can be difficult to demold, and automated structures like lifters and sliders are rarely used, making it inefficient for parts with negative angles or side holes.

It is used for manufacturing large exterior parts with simple structures but high strength requirements, such as air deflectors, side skirts, and truck front bumpers. Highly applied in the commercial vehicle sector.

As more new forces enter the automotive manufacturing industry, the diversified internet-thinking elements they bring are reflected in vehicle creation. Consumers are adapting to these diverse vehicle styles, requiring traditional automakers to speed up their innovation; otherwise, they risk being abandoned by the market.

In the early stages of vehicle development, manufacturing rapid interior and exterior prototypes to assemble concept cars for display and making design adjustments based on market feedback provides an opportunity for trial and error. This can save a massive amount of development funds and shorten the development cycle. Therefore, rapid prototyping will remain an indispensable phase of whole-vehicle development for a very long time.