Machine Selection

It is axiomatic that anyone who has production responsibility for a brazing process has the objective of improving one or more of the following features of his particular process:

1. Productivity 2. Product quality

3. Quantity produced per unit time 4. Process repeatability

At the same time there will also be an imperative to minimize the impact of two other inherent features of the process:

1. The skill level needed by the operator 2. The unit cost of producing the part

Faced with these desirable objectives it is all too often the case that the engineer who has responsibility for the process becomes affected by a kind of euphoria. This can cause him to embark on a route that inexorably leads to the purchase of a highly sophisticated machine that may provide him with the entire weekly requirement of finished parts in the space of a few hours. Such a solution is certain to be technologically pleasing but it will

FIGURE 5.15

A pick-and-place unit being used to remove a refrigerator compressor body from a rotary indexing brazing machine. (Courtesy of VerMoTec GmbH, St. Ingbert, Germany.)

certainly fail to be the most cost-effective solution to the process under review.

Table 5.1 shows the detail of the flame brazing complexity scale. Before determining how far up the complexity scale a person needs to go, he must first undertake an audit of his process in order to determine where he is now. This is best done by a systematic assessment of the situation in accor-dance with the criteria detailed in Chapter 12.

With the assessment is complete, it will then be possible for the engineer to establish the true economics of his current procedure; he will be in a position to calculate what changes he can afford to make in order to attain the maxi-mum cost-effectiveness from the process. It cannot be overemphasized how useful such a procedure is; it is a worth-while exercise even if it does nothing more than force the engineer to consider the detailed steps that he needs to take in order to achieve his objective. Generally, an engineer will find that there are some gaps in his knowledge, and these can be filled by the simple expedient of a detailed discussion with the technical specialists of his supplier of filler materials; of course much, if not all, of the information that he will need can be found in this book. In order to be in position to assess the various options available, the engineer needs a frame of reference that will provide him with some guidelines concerning the type of machine that, in all proba-bility, will provide the best-practice solution to the project under review.

There are four broad parameters that need to be considered:

1. The number of parts per hour that need to be produced 2. The component configuration

3. The type of fixturing required

4. The heat pattern that will be needed in order to effect the joint

5.2.4.1 Number of Parts to be Produced

There is a fundamental relationship between the number of parts and the number of joints that have to be produced when deciding which particular machine type should be selected.

Where the component to be brazed consists of only two parts and is required at a rate of 180 pieces per hour or less, a trolley system or a manually indexed machine is needed. If the output rate demanded is higher than 180 pieces per hour, then some form of mechanically driven rotary machine or an in-line conveyor will be the appropriate choice. If the assembly comprises three or more parts and the required production rate exceeds 180 pieces per hour, the matter of machine selection becomes somewhat more difficult. In such situations it is necessary to take two further factors into account:

1. The time taken to assemble the parts and load them into their jigs (Remember, the assembly time might need to take account of flux and alloy application to the joint areas.)

2112_book.fm Page 139 Tuesday, November 4, 2003 1:07 PM

1. If assembly and loading time is more than four times longer than the heating time, some form of trolley machine is required.

2. If assembly and loading time is less than four times the heating time, the choice of machine lies between rotary indexing and a trolley. The type that is finally chosen is dependent on other factors that are mentioned in Section 5.3.

3. If the heating time is longer than the assembly and loading time, some form of rotary indexing machine is used. If the components are self-fixturing, it might be possible to opt for a continuous in-line or rotary machine.

5.2.4.2 Component Configuration

If the part to be brazed is bulky, required at a relatively low output rate, and has two or more joints at widely separated points on the assembly (e.g., a frame of some type), the natural choice would be a trolley machine. If a high rate of production is required, it is probable that a rotary indexing machine would be selected.

5.2.4.3 Fixturing

If the fixturing is complex and requires the workstation, and hence the work track, to be at rest while the components are loaded into their fixtures, some form of trolley or rotary indexing machine will be required. The selection between these two types of machines will depend on other criteria (e.g., component configuration and the hourly output rate required.

5.2.4.4 Heat Pattern

If the components require heating from both sides, any machine type, except the small continuous rotary machine that applies heat only from the outside, can be used.

5.3 Summary

To summarize, the intelligent application of the four basic criteria men-tioned above would reveal which machine type should be selected for any given job. As has already been mentioned, the ultimate in mechanised flame

brazing will only be achieved if a rotary indexing or in-line indexing machine is employed and a number of subsidiary operations can be carried out as an integral part of the overall brazing process. Since it is self-evident that the selection of an indexing machine of any type presupposes large volume production and probably complex jigging the selection of an in-line indexing system will almost never occur for the reasons outlined earlier (see Figure 5.7 and its associated text).

It follows that the mechanization of subsidiary operations such as assem-bly and loading, the application of the brazing materials, and automatic part ejection, is nearly always associated with rotary indexing equipment.

However, there are examples where trolley machines have been con-structed that incorporate automatic wire feeding to several widely sepa-rated joints at the brazing station. It is not possible to specify when ancillary mechanization devices should be incorporated. As a guide, about 40% of modern rotary indexing machines incorporate automatic wire feeding, 30%

incorporate both wire feeding and automatic fluxing, and 20% use auto-matic brazing material application and subsequent autoauto-matic removal of the brazed parts.

The higher the degree of mechanization, the greater will be the capital cost and the lower the degree of flexibility possessed by the system (see Figure 5.2). The machine’s cost needs to be amortised within the timescale dictated by the policy of the company that is planning to purchase it. This factor, balanced against the needs of productivity and technical excellence, will ultimately determine the degree of mechanization that can be afforded. By undertaking a detailed technical analysis of the process, the engineer can be satisfied that he understands the fine points of why a particular solution to a specific production brazing problem was adopted.

The outcome of such an analysis might indicate that the problem can only be resolved by the installation of a piece of equipment that incorporates every imaginable type of ancillary mechanization device that human inge-nuity can device. Such an outcome is highly unlikely, but most specialist brazing machine builders tend to hold the view that such a miracle will eventually occur.

2112_book.fm Page 141 Tuesday, November 4, 2003 1:07 PM

6