Blending Rapid Tooling with Conventional Moldmaking

The issues of if and when to use rapid tooling (RT) are becoming critical topics in the manufacturing community.

With rapid tooling (RT) technologies emerging and the increasing demands put on toolmakers, the issues of if and when to use RT are becoming critical topics in the manufacturing community. The world of conventional toolmaking is faced with an increasing list of problems, the first being increased competition - local and foreign. Customers also are adding to the tension by increasing the demand to produce tools faster than what was considered good even a few years ago.

Another source of frustration can be the decreasing employment trends in many parts of the world. There is a shrinking pool of skilled labor coupled with fewer people entering the toolmaking field. For these reasons the industry is interested in RT, and curious how and when the many processes work. For the purposes of this article, the term "rapid tooling" does not include tooling generated from CNC or traditional metal removal techniques.

To begin discussing RT, the first thing to have is an open mind. There is a fear that exists with many people in the toolmaking field because these processes are new and different. Many view RT as an unknown, unproven and risky endeavor. This is not to say that all of the methods are fully proven and commercialized, but many of these techniques are fully capable of filling a need if the criteria are a good fit.

Any discussion of RT processes must begin with a realization that each process has its own unique set of advantages and disadvantages. RT is not only a process change, but also a philosophy change. With this in mind, willing toolmakers must realize that some of their basic assumptions about the tool building process must change. As an example, consider a customer who wants to modify the part design soon after the preliminary tool design has been approved. In the traditional tool shop the change is most likely easy to integrate.

The steel has been ordered and may even be in production, but usually the part geometry is not completed. The same example being applied to RT causes a different situation. If the tool cavities are being made through DTM's RapidSteel, then the first stage is to build the cavities and cores on a Selective Laser Sintering (SLS) machine. In this example the most critical stage of the tool is created first, and any changes could be costly. For this reason the communication and contact with the customer are an integral part to the success of many RT projects. Many details such as shrink rates and engineering changes need to be determined as early in the process as possible. This can be a challenge since many of the best applications are fast turnaround prototype tools.

Early in RT development it became apparent that there was not one single process that would suit all of the company's goals or the customer's needs. For this reason RT technology must be a constant search for new processes and the improvement of existing processes. In almost all cases new RT methods must be evaluated. It has been found that some are immature or not fully "dialed in." Occasionally, a new process is developed that will meet or exceed user needs or show improvement over a similar technique.

*Please note that this article does not cover all of the RT processes currently available, it merely shows how some of the processes have enhanced toolmaking abilities. It also must be stated that just because the representative company does not use a certain RT process, does not mean that it has no benefit or worth. It just means that every RT process has its application.

Following are three types of RT techniques.
1. Development Tooling: The fastest and generally lowest cost tooling solution. Delivery of one to three weeks and a tool life of at least 50 to 200 parts.
2. Mid-Range Tooling: This type of tooling offers a fast turnaround and consistent tool tolerance. Delivery of two to five weeks and a tool life ranging from 200 to 10,000 parts.
3. Low-Volume Production Tooling: This tooling method will serve as a production tool for less demanding applications. Delivery of four to six weeks and a tool life of 10,000 to 100,000 parts.

In order to decide how to match a tooling project with a tooling process, each part must be evaluated and measured by certain general and specific criteria. The general criteria to exact a method are part size, part geometry, part tolerance, plastic material, number of shots required and delivery demands.

Today's RT Situation

There is little doubt that today's RT technologies are still in a state of infancy. Although a few skilled companies have worked through the learning curve and are using RT on a commercial basis, most of them are reluctant to rely on it for other than testing or sporadic projects. The fact is that RT can already be a good fit for a large percentage of prototype tools and a growing number of production tools.

Although the RT processes are maturing there are still quite a few difficulties. To master the use of RT, a unique set of qualities must be present. The successful users must have the knowledge and experience of 3-D solid modeling, rapid prototyping, toolmaking and blend them all with the skills of an artisan. Below is a list of general strengths and weaknesses of current RT processes. While not all of the current methods share every strength and weakness, it is fair to say that they will share the majority of the characteristics.

Rapid Tooling Strengths
1. Speed: Most RT processes can provide an increase in speed over conventional tooling methods; however, this is mostly true on smaller and more complex geometries. For example, a typical core geometry that includes extensive ribs and bosses typically will take many operations including CNC programming, CNC milling and EDM. However if the same core fits into the qualifications for RT, then it can easily be built in one operation.

2. Cost-effectiveness on complex tooling: The processes lend themselves more to complex geometries that would be difficult to manufacture traditionally. This is partly due to the high costs of equipment required for the RT techniques.

3. Automation: Many of the RT processes are highly automated. This means that the users can run the equipment and build tooling sets 24 hours a day, seven days a week including holidays. It's more than just the productivity of the RT process that is improved; it's the productivity of the whole shop. It can provide the tools to output much more work than the size of your shop or your manpower will conventionally allow.

4. Human error: RT processes eliminate a certain amount of human error found in conventional toolmaking processes. By automating the cavity and core building process to build directly from the original solid model, human error can be reduced. Examples can range from the misinterpretation of blue prints, to incorrect and inaccurate setups on a CNC mill.

5. Build multiple cavity/core sets: Additional cavity and core sets can be built with a first set at a reduced cost. Sharing overhead costs on either multiple cavity or multiple customer projects can increase the cost effectiveness of many tooling projects.

6. Creative design possibilities: RT techniques share a quality that the tool cavities are created unconventionally. This offers the unique possibility that the design can be custom tailored to take advantage of the build process advantages. An example of this would be to integrate conformal cooling channels into a complex core design. The possibilities are not limited to creating a design that is conventionally machinable.

Rapid Tooling Weaknesses
1. Accuracy: Most RT processes have a best case tolerance around q.005" to q.010" range. It is standard procedure to design extra stock on critical dimensions and seal-off conditions to be tuned in traditionally. However, this extra step can hurt the effectiveness of the process.

2. Cost-effectiveness on simple tooling: The cost of materials and equipment has created a high overhead associated with most RT techniques. This can quickly rule out many projects if they are relatively easy to produce conventionally.

3. Size limitations: Many of the RT methods are limited in the physical size of inserts that can be effectively created. Most processes have a maximum cavity size of less than 10 square inches.

4. Tool life: Most RT options have a limitation of tool life due to the materials of the cavity inserts. This can be affected by the end product material and possibly enhanced by surface coatings or treatments. This can be an important criterion for selecting an RT process.

5. Investment in equipment: RT techniques generally require a significant investment in capital equipment if a company wants to perform the work in-house.

The Future of Rapid Tooling

As development progresses in the area of RT, the existing processes will continue to eliminate its weaknesses and improve its strengths. While this is taking place, new methods are continually being explored - offering the possibilities of even more excitement. As this future becomes reality, these new methods will further enhance the usefulness and acceptance of RT into the toolmaking community. While the industry also is changing and becoming more competitive, RT should not be seen as an enemy. It should be viewed as another weapon in our arsenal for becoming better toolmakers. This can be equally as important for the large OEM trying to get its product to market faster and the small mold shop fighting to compete.

 

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