13.1 Quality Improvement Concepts, Products & Processes

Detection Versus Prevention

Two philosophies of quality sit behind every decision an inspection department makes.

Detection finds defects after they have been created. Sorting, screening, final inspection, and containment are all detection activities. Detection is necessary — it protects the customer — but it has three permanent limitations:

1. It adds cost without adding value. The customer pays for a good part, not for the act of separating good parts from bad ones.
2. It is imperfect. As established in section 9.4, sustained manual visual inspection is only about 80% effective.
3. It happens after the money is spent. By the time an inspector finds a defect, the material, machine time, labor, and often several downstream operations have already been consumed.

Prevention stops defects from being created. Capable processes, error-proofing, robust design, controlled inputs, trained operators, preventive maintenance, and statistical process control are prevention activities.

W. Edwards Deming's formulation is the one the exam expects: "Cease dependence on inspection to achieve quality." You cannot inspect quality into a product; quality has to be built in. Deming also argued that the large majority of problems originate in the system rather than in the individual worker — the point he expressed as the 85/15 rule and later revised toward 94/6. That principle is why corrective action targets the process and not the person, and why blaming an operator for a nonconformance is almost always the wrong root cause.

The practical inspection-department consequence: inspection data is most valuable as process feedback, not as a sorting mechanism. The measurements you record are the raw material of control charts, capability studies, and corrective action.

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The Cost of Quality and the Cost of Poor Quality

The cost of quality (COQ) framework, usually attributed to Armand Feigenbaum and popularized by Joseph Juran and Philip Crosby, sorts all quality-related spending into four categories known as the PAF model plus failure costs.

Two classification questions are exam staples:

• Calibration is an appraisal cost. It exists to make evaluation trustworthy. Training is prevention; inspection and calibration are appraisal.
• Re-inspection after rework is an internal failure cost, not appraisal, because it would not exist if the defect had not occurred.

Cost of poor quality (COPQ) is conventionally the internal plus external failure categories — the money spent purely because things went wrong. Total cost of quality across all four categories is commonly quoted at roughly 15% to 25% of sales in organizations that have not systematically attacked it.

The Economics That Drive Prevention

The 1-10-100 rule is the widely used rule of thumb: a defect costs roughly 1 unit to prevent at the source, 10 units to find and fix internally, and 100 units to deal with once it reaches the customer. The exact multipliers vary by industry and the numbers are illustrative rather than measured, but the direction is universally true and it is what justifies spending on prevention.

The hidden factory (Feigenbaum's "hidden plant") is the related idea that a substantial fraction of a plant's capacity is consumed producing, finding, and fixing defects — capacity that never appears as a line item because rework is absorbed into standard cost.

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Total Quality Management

Total quality management (TQM) is a management approach in which quality is the responsibility of the entire organization rather than a department, and improvement is continuous rather than episodic. Its recurring principles:

• Customer focus. Requirements are defined by the customer, internal and external.
• Total participation. Everyone contributes, from the executive suite to the operator.
• Process focus. Results come from processes, so improve processes to improve results.
• Continuous improvement. Small improvements compound; there is no finish line.
• Fact-based decisions. Data over opinion.
• Management commitment. Without leadership resources and attention, quality initiatives fail.

TQM as a branded program has largely been absorbed into ISO 9001 quality management systems, Six Sigma, and lean, but the exam still tests it by name and expects familiarity with the thinkers behind it.

Taguchi's loss function deserves the inspector's attention because it contradicts the goalpost thinking that tolerances encourage. Under a "conforming or not" view, a part at 0.0009 in from nominal within a 0.0010 in tolerance is as good as one at nominal. Taguchi's view is that loss increases continuously with departure from target, so a process centered on target is genuinely better than one that merely stays inside limits — the same argument that makes Cpk more informative than a simple pass rate.

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Customer Satisfaction

The customer is whoever receives the output. Every organization has both:

• External customers — the purchaser, the end user, and regulators.
• Internal customers — the next operation, the next department, the next shift. "The next process is your customer" is Ishikawa's phrasing, and it is what makes an inspector's disposition decision meaningful: releasing marginal work to the next operation is exporting a problem to a customer.

Voice of the customer (VOC) is the collection of stated and unstated customer requirements through complaints, warranty data, returns, surveys, scorecards, and direct contact. A quality inspector contributes to VOC in a concrete way: customer complaints and returns arrive as nonconformance and corrective action inputs, and the inspection records the shop already holds are the evidence used to answer them.

The Kano model classifies requirements by how satisfaction responds to performance:

Kano's dynamic matters: today's delighter becomes tomorrow's expectation. Statistical process control data supplied with shipments was once a differentiator and is now a baseline requirement in automotive and aerospace supply chains.

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Products and Processes

Body of Knowledge topic IV.A.2 asks you to distinguish these and to describe how they interrelate.

Definitions

Following ISO 9000:

• A process is a set of interrelated or interacting activities that use inputs to deliver an intended result.
• A product is an output of an organization that can be produced without any transaction taking place between the organization and the customer — a physical thing, generally.
• A service is an output with at least one activity necessarily performed between the organization and the customer.

The distinction that matters practically: you inspect a product, but you control a process. Product inspection tells you about the units in front of you. Process control tells you about the units you have not made yet. Only the second one is predictive.

The Process Model

Every process can be described as inputs, activities, and outputs, with the SIPOC framework naming the full chain: Supplier, Input, Process, Output, Customer.

Inputs to a manufacturing process are conventionally grouped by the 6Ms used in the fishbone diagram in section 12.1: Man (people), Machine, Material, Method, Measurement, and Mother Nature (environment). Each is a place a defect can enter.

How Design, Material, Process, and Output Interrelate

The BoK asks specifically how individual steps affect the final product and the system as a whole. Three relationships explain most of it.

1. Design constrains everything downstream. A tolerance that is tight relative to the capability of any available process guarantees scrap no matter how well the shop performs. A design that requires an impossible tool access guarantees a manual operation with high variation. Roughly 70% to 80% of a product's cost and much of its quality is determined at the design stage, which is why design FMEA and design review precede production.

2. Material properties propagate. A heat of steel at the high end of its hardness range machines differently: tool wear accelerates, dimensions drift faster, surface finish degrades, and the process capability the shop demonstrated on a previous heat no longer applies. The inspector who sees dimensional drift and hardness variation together in the same week is looking at one cause, not two.

3. Upstream variation compounds downstream. Consider a shaft:

Every step measured on its own could pass. The final output fails because deviations accumulated and interacted. This is the systems view the BoK is testing: an inspector who reports only "final dimension out of tolerance" has recorded a symptom, while one who reports the dimensional history across operations has handed the corrective action team its root cause.

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Common Exam Traps

• Calibration is appraisal, not prevention. Training and error-proofing are prevention.
• Re-inspection after rework is internal failure, not appraisal.
• COPQ is normally the failure categories only, while COQ includes prevention and appraisal as well.
• You cannot inspect quality into a product. Any answer that solves a systemic quality problem by adding inspection is suspect.
• Deming assigned most problems to the system, not to the worker.
• Crosby defined quality as conformance to requirements, not as goodness, luxury, or elegance.
• Juran named the Pareto principle; Pareto himself studied income distribution, not defects.
• Taguchi's loss function is continuous. Loss begins at departure from target, not at the tolerance limit.
• Products are inspected; processes are controlled. Only process control is predictive.