It is widely known that platinum, the most noble of metals, is also the most challenging of metals.  Thus, in trying to determine a suitable topic for the presentation on Platinum Day, we asked ourselves what single most important element contributed to the success we have experienced.  We also asked ourselves what single most important element could benefit the jewelry industry in general, not only those engaged in casting platinum.

The topic that emerged from our brainstorming was unequivocally "a controlled process." Platinum's high level of sensitivity to even the tiniest variation in processing was something we had experienced first hand, and as most things of high value, had to be learned the hard way.  Numerous, painstaking sessions of defect analysis and the resulting mountains of documentation have led us to where we are today.  We now maintain a controlled process with yields upwards of 95%.

In order for a process to be valuable and powerful, the process must produce acceptable products consistently and predictably. To accomplish this, the process needs to be in control at all stages.  A controlled process may be defined as a directed and consistent application of people, materials, equipment, methods and environment to produce a product.

The Value of a Controlled Process
There are many reasons that a controlled process is a valuable asset for platinum casters. A controlled process provides an index of capability for any level of production. It also boosts internal efficiencies and reduces scrap and rework.  Additionally, it can help a company adapt to changing products and technologies.  Finally, unlike product design, it is far more difficult for competitors to duplicate.

Characterizing a Process
A truly powerful process is not one that defines quality in terms of rejects after all manufacturing operations have been completed. It is a process that creates a very high percentage of acceptable product and is monitored, analyzed and documented at every stage. It is important to keep in mind that the most current models of production extend the process both "upstream" and "downstream" to include customer satisfaction on the one end and employee training and raw material control on the other. The key to habitually producing high quality castings lies in discovering the optimum operating parameters for each stage in the process and then performing the operations in precisely the same way every time. In other words, the people, materials, equipment, methods and environment must be well defined and well controlled. The aim of a controlled process is not to compile charts and records, but to make a defective casting a process improbability.

The first step in controlling the process is to characterize all of the variables that can affect the output.  To determine the process interactions, it is necessary to draw a "process map" to diagram the flow of products through the process. Once this is accomplished, the variables of control must be determined for each stage.

The process map then can be taken a step further to provide a strategic plan for control of related variables. The process variables can be outlined in their proper sequence and the actual techniques and conditions to be maintained are related to the individual stage of the process in the process analysis chart.

In the process analysis chart, there are variables listed for possible control.  It is important to remember that the measurement of each variable will need to be done with a controlled and calibrated instrument to ensure that the recorded variable values reflect the item being measured and not the wear and tear of the measuring device.

It is important to note that characterizing the process will not inherently improve the process; however, it will permit a basis for correction when problems arise.  Once the entire process has been characterized and analyzed for variables that require monitoring, standardizing and documentation, the next step is to initiate control of these factors. It is only after the variables are controlled that the process can be optimized and improved.

Process Control
The tools of process control are the documented procedures, the attribute chart and the control chart. In order to control a process, it is necessary to direct and consistently apply all the process variables. In a classical sense, "this consists of observing actual performance, comparing this performance with some standard and taking action if the observed performance is significantly different from the standard." The imposed standards must be representative of a highly capable process and be documented to clearly outline what the outcome must be.  To establish the proper standard for each process variable, specific performance criteria will be in the form of process instructions or operational techniques.  These techniques will need to be designed with clear an understandable directions to perform the operation. They need to be written in a "step—by—step" manner with all relevant instructions listed.  This is generally not the place for theoretical considerations. Prescribed and proscribed activities with necessary precautions are the only details that should be included in a process instruction.

Sometime the performance criteria will be measured data that represents a necessary condition (attribute). Historical information will establish the correct standard for this type of data. Attribute data is usually viewed as a "yes/no" or "go/no go" condition.  It can be recorded and controlled on a simple checklist that confirms the required status of a variable.

Finally, sometimes the performance criteria will be measured data that can be of any value.  Variable data needs to be recorded on a control chart. Historical data can be used to calculate the average value of a variable when the process is in control. To control variable data, the measure must be taken and recorded on the control chart. If the value of the measurement is beyond either the upper or lower control limit, the process must be stopped until the condition is corrected and the variable can demonstrate a measure within normal variability.  Once the control limits are in place, controlling variable data is as easy as controlling an attribute or following a clear instruction.

The tools of process control need to be applied to all identified variables in each stage of the process.  However, a variable may be measured in a variety of ways. To limit the number of tests and measurements that are used to control a specific portion of a process, it is necessary to define the key control characteristics which actually can affect the quality of the output. These will vary from process to process, but a realistic focus on the factors of the process (people, methods, materials, equipment and environment) at each stage should help limit the quantity and type of the control variables.

People: The most important way to control this significant process factor is to determine the knowledge, abilities and skill levels required to perform the process operation.  Once a person has been determined to have the prerequisite qualifications, they must be properly trained to do the job. The general guideline for people performing a process is to:  1) ensure an adequate skill level; 2) provide them with unambiguous instructions for which they are supposed to do; 3) give them feedback about there performance; and 4) arrange a means for regulating their performance with corrective action.

Methods: Closely allied with people are the methods they employ to process manufacturing inputs.  These include all the process instructions as well as all the systems in place that guide the process. Methods to set up, run and maintain equipment are also included in this consideration.  Specifications for testing, inspection acceptance and the way customers expectations are integrated into the final output are all methods of the manufacturing operation.  Corrective action programs and continuous improvement strategies are all encompassed in the methods of a process.

Materials: All raw materials in a stable process must be of a known and consistent quality. The suppliers of wax, investment, binders and metals must certify the components and characteristics of the materials they supply. A controlled process needs to record and track this data to guarantee the quality of the supplied raw materials.

Equipment: All equipment used in a process must be appropriate for the task.  The function of equipment must also be well maintained and consistent in operation.  All these functions must be periodically checked and calibrated to attest that the equipment continually works to specifications.

Environment: It is already broadly accepted that temperature and humidity need to be controlled during wax assembly and investing. Also, certain platinum alloys may require an inert environment during melting. It must be remembered that environment additionally includes things that do not directly envelope the castings.  Items like safety, housekeeping and empowerment of workers may be hard to measure, but these can certainly impact the quality of the process output.  It is the overall environment that will direct a controlled process to continuous optimization.

Process Optimization
Process optimization means that corrective action is applied when non—standard variation or defects are detected and that the process is improved by design.  The quality of the output provides the requisite feedback about the effectiveness of the process.  The feedback becomes a tool to correct problems as they arise and to improve overall quality of the process itself. To obtain the greatest value from a controlled process, it is necessary to take advantage of the feedback provided from the products in the form of defect analysis and process improvement.

Defect Analysis
Most platinum casters have experienced all types of problem despite the most stringent controls. Nevertheless, some defects can actually help a caster pinpoint problems in a process by identifying the root cause.  This is the main focus of defect analysis where problems with the outcome are used to uncover greater than normal variations (special conditions) in the process.
After the defect has been categorized and the process stage which could have caused it has been identified, a careful examination of the variables in question must take place.  A useful tool to accomplish this is the "fish—bone diagram." by relating individual conditions to each of the factors of the process stage, the defect analysis can be more complete and thus, fruitful. This type of investigation will help sustain a capable process.

Process Improvement
While defect analysis can sustain and fine tune a capable process, process optimization provides more than mere sustenance.  It requires deliberate action to reduce variability through process improvement.  Through designing process improvement experiments, a company can "determine the optimum settings of the factors that control a process."

It has been said that if you can make only one good part out of a thousand then the process can be made capable of producing 100%.  The hard part is to find the optimum conditions for the process to be fully capable.  There needs to be a continual and regular deployment of designed experiments in the process in order to ensure continuous improvements.

In conclusion, a controlled and powerful process pursues investment casting as a science, not an art.  Casting platinum requires that all the scientific methods available will need to be deployed.  Detailed characterization, control and optimization of the investment casting process is the only way to create a process that will meet the needs of exacting customers.  The right process can be created with never—ending devotion to detail.  It has been well established that, "the process of installing quality improvement is a journey that never ends."
 

V4N2

Platinum Casting:  The Power of Process Control
Helmut F. Frye Ph.D.
Timothy L. Donohue
TechForm
Advanced Casting Technology, L.L.C.

This is an abbreviated version of the original work. For full technical details, please consult the original paper.