SECTION 1.4
The Design Process

While some of the specific aspects of a broach tool will be discussed in subsequent sections, there are a few basic principles and procedures that should be introduced at this point. The design process consists of these basic steps:

1. Initial summary of the design problem.
2. Analysis of the design requirements.
3. Development of preliminary ideas.
4. Development of alternatives.
5. Finalization of design.

While these steps are separated for this discussion, in practice each of them actually overlap the others. For example, when stating the problem, the requirements must also be kept in mind to properly define and determine the problem or task to be performed. Likewise, when determining the initial design ideas, the alternative designs are also developed. So, like many other aspects of manufacturing, broach tool design is actually an ongoing process of creative problem solving.

SECTION 1.4.1
Summarize the problem

The first step in the design of any broach cutting tool is to define the problem as it exists without tooling. This may simply be an assessment of what the proposed tool is expected to do, such as broach an elongated hole. Or, it may be an actual problem which has been encountered in production where broach tooling may be beneficial, such as low volume production output caused by a bottleneck in a milling operation.

Once the exact extent of the problem has been determined, the problem can be analyzed. Once analyzed, the problem can be resolved throughout the remaining steps of the design process.

SECTION 1.4.2
Analyze the design requirements

After the problem has been isolated, the specific requirements such as function, quality, cost, delivery, and other related specifics can be used to determine the specific parameters within which the designer must work. Every broach tool that is designed must (1) perform certain functions, (2) meet certain precision and accuracy requirements, (3) keep the cost to a minimum, (4) be available when the customers' production schedule requires it, (5) operate safely, and (6) meet various other requirements, such as adaptability to the machine on which it is to be used, or have an acceptable working life.

Figure 1-1 on the next page shows a method of applying these criteria to the process of choosing a tool design. Rarely, if ever, will one tool design be best in each of the five areas shown. The broach tool designer's task here is to weigh all these factors and select the design that best meets these criteria and the task to be performed. As you can see in the figure, option A presents the best alternative (the highest total provides the best option; the higher the value of each factor, the more appealing that factor is to the customer). Although option B rates highly in terms of function and quality, the cost and delivery make it prohibitive. The opposite is true for option C.

SECTION 1.4.3
Develop preliminary ideas

Initial design ideas are normally conceived after an examination of the preliminary data. This data can be seen on the Key Information (New Broach Designs) form at the end of this section. While evaluating this information, the broach tool designer should take notes to insure that nothing is forgotten during the initial evaluation. Should the tool designer need more information than that furnished with the design package, the sales agent, engineer, or planner responsible for the tooling request should be consulted to determine the required additional information. In many cases, the tool designer and planner must jointly develop parameters during the initial design phase.

SECTION 1.4.4
Develop design alternatives

During the initial concept phase of design, many ideas will occur to the tool designer. As these ideas are thought out, they should also be written down so they are not lost or forgotten. There are always several ways to do any job. As each method is developed and analyzed, the information should be added to the list shown in Figure 1-1.

Figure 1-1.
A basic model for tool design analysis

SECTION 1.4.5
Complete design ideas

Once the initial design ideas and alternatives are determined, the broach tool designer must analyze each element of the design to determine the best possible way to proceed toward the final tool design. As was stated earlier, rarely is one tool alternative a clear favorite over any other. Rather, the designer must evaluate the strong points of each alternative and weigh this value against the weak points of the design. For instance, one design may have a high tool life but the cost of the tool may be very expensive. On the other hand, a second tool may provide less life but will cost much less to build. In this case, the value of the production rate might be the factor used to determine which will be the best design for the job.

If the job is a long term production run, the first broach tool may pay for itself in increased tool life. If, however, the production run is short or is a one time run, the second broach tool may work best by sacrificing tool life for a reduced tool cost. Seldom will one tool be able to meet all the expectations of the tool designer. In most cases the best design is a compromise of the basic criteria of function, quality, cost, due date, safety, and other requirements.