By Walker Woodworth, President of Frank Roth Co.
Process control is essential for successfully manufacturing complex machined parts. Whether producing high volumes or short runs, consistent results require control, discipline, and a structured approach to defining and executing machining processes. When processes are loosely defined, variation fills the gap—and consistent quality becomes elusive.
This is where the principle “Pin it down, Lock it down” applies. Pin it down means “define the machining process in detail—requirements, sequence, tooling, inspection, and identification of risks—before production starts.” Lock it down means “validate the process, controlling changes, and execute it consistently on the manufacturing floor.” Advanced Product Quality Planning (APQP), a well-defined approach, provides the structure to do both. Used correctly, it forces critical thinking, reduces avoidable variation, and keeps quality under control from the first articles manufactured through the completed production run. While APQP is used significantly in the automative industry for high-volume production, I believe strongly in its techniques for mid to small lot sizes when consistent quality is critical and risks must be mitigated.
Steps to Pin It Down
1. Planning and Feasibility
Requirements must be clear and achievable before releasing a machining process.
Pin it down by:
- Confirming drawing requirements, tolerances, special characteristics, and inspection methods.
- Verifying machine capability against critical tolerances – prove your process is capable.
- Identifying high-risk features, operations, and assumptions.
- Resolving open issues before tooling or programming begins.
- Understand how the part fits into the overall picture – what’s it used for? What does the part mate with? How does the customer evaluate the part or assembly?
If feasibility is uncertain, the process is not ready to move forward.
2. Process Definition
This step defines how the part will be made.
Pin it down by:
- Documenting the full process flow, including secondary operations and inspection.
- Standardizing fixtures, tooling, and setup methods. – Specify everything; leave nothing to chance.
- Defining critical process parameters and where variation can enter.
- Capturing known issues from similar parts.
If the process depends on tribal knowledge, or if it is left to interpretation, it is not pinned down.
3. Risk Analysis
Machining risk is a given. Tools can chip, fixtures can fail, inspection instruments can wear. Process Failure Modes and Effects Analysis (PFMEA) should address risk directly.
PFMEA sounds like a lot of work, but a few hours of prevention can point out potential problem areas and give you valuable insight regarding how to make your process more robust.
Pin down risk by:
- Identifying realistic failure modes—wear and tear on tools and fixtures, mistakes in offsets, and gage error.
- Ranking risk honestly based on customer impact and escape potential.
- Implementing preventive controls. – Detection alone isn’t enough.
Every process has weak spots. If PFMEA actions do not change your process, risk is not controlled.
Steps to Lock It Down
1. Process Validation
After the process is defined, it must be proven.
Lock it down by:
- Running trials at planned rates using production tooling.
- Completing first article inspections.
- Understanding how long your tooling lasts.
- Plotting your key measurement data and really analyzing it. – No process remains perfectly stable forever. Find out where it goes awry and why it becomes unstable. Then either reduce the risk or find a way of monitoring the problem area.
- Verifying measurement systems and locking down the approach. – If there is measurement system variance anywhere, it should be analyzed to ensure it won’t crowd out true measurement data.
- Substantiating any supplier variance.
- Verifying all customer measurement techniques and correlating your own measurement process to their techniques.
A process is not ready for production if the variance in measurement systems is too great and it cannot hold tolerance during validation.
2. Production and Control
After launch, stability matters more than optimization. I’ll take a stable process that requires a longer cycle time over one with a fast cycle time but significant variance any day of the week.
Lock down your process by:
- Creating a culture that embraces the effectiveness of control plans.
- Defining clear reaction plans for out-of-control conditions.
- Managing tooling, offsets, and inspection changes through formal approval and training.
- Updating the PFMEA and control plans when changes occur or when you run into a quality issue.
Uncontrolled change leads to losing process control—and your sanity!
Final Thoughts
In machining, APQP is effective when you encourage a company culture that embraces the approach and recognizes its value rather than viewing it as just inconvenient paperwork.
- Pin it down by defining the process and risks before production.
- Lock it down by validating capability and controlling change.
Doing so improves everything—quality becomes predictable, customer satisfaction increases, and you prevent problems instead of merely managing them. Ultimately, this all leads to stronger customer relationships, elevated profitability, and more opportunities for growth.
If you’d like to dig deeper into how the pin it down/lock it down M.O. of APQP ensures successful manufacturing results, feel free to contact us.
