1.3 Customer-Supplier Relationships & Quality Culture

1.3 Customer-Supplier Relationships & Quality Culture

The Customer-Supplier Chain: Internal vs. External Customers

Traditional manufacturing models viewed quality as a simple transactional relationship between the external company and the end-user purchasing the finished good. Modern quality engineering expands this horizon through the Customer-Supplier Chain, recognizing that customer relationships exist at every step inside the manufacturing plant.

External Customers

An external customer is an individual, business entity, or government agency that purchases or uses the organization's finished products or services. External customers define commercial market requirements, hold legal contracts, pay invoices, and experience the final product's reliability in field service.

Internal Customers and Suppliers

An internal customer is any employee, operational work center, assembly cell, or administrative department within the enterprise that receives materials, components, data, or services from an upstream work center (internal supplier).

• The heat-treatment department is an internal customer of the rough machining cell.
• The deburring department is an internal customer of the stamping press.
• The final packaging department is an internal customer of the dimensional inspection lab.

Building upon Kaoru Ishikawa's rule that 'The next process is your customer,' every technician and operator must treat downstream workstations with the same rigor, responsiveness, and zero-defect standard as an external commercial client. If an internal supplier ships out-of-tolerance stampings with heavy burrs to the assembly cell, assembly must waste time hand-filing parts or suffering line shutdowns, destroying throughput.

[External Suppliers]
         |
         v
[Receiving Inspection]  --> (Internal Customer of External Supplier / Internal Supplier to Machining)
         |
         v
[CNC Machining Cell]    --> (Internal Customer of Receiving / Internal Supplier to Deburring)
         |
         v
[Deburring & Wash]      --> (Internal Customer of Machining / Internal Supplier to Assembly)
         |
         v
[Final Assembly & Test] --> (Internal Customer of Deburring / Internal Supplier to Shipping)
         |
         v
[External Customers]    --> (Final End-Users, Regulators, and Commercial Clients)

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Voice of the Customer (VOC) Methodology

The Voice of the Customer (VOC) represents the explicit and implicit requirements, expectations, preferences, and dissatisfaction signals communicated by customers. VOC data drives Quality Function Deployment (QFD), new product development, and inspection planning.

Translating VOC into Critical to Quality (CTQ) Parameters

Customers rarely describe their requirements using engineering tolerances. They use subjective, functional language. Quality technicians and engineers must translate subjective VOC statements into objective, measurable Critical to Quality (CTQ) technical specifications:

• Customer Statement (VOC): "The adjustment knob feels loose and rattles when I operate the unit."
• Technical Translation (CTQ): Radial shaft runout specified as $\le 0.001\text{ in}$, with shaft-to-bore diametral clearance controlled at $+0.0005\text{ to }+0.0012\text{ in}$, verified using a dial test indicator.

Proactive vs. Reactive VOC Gathering Methods

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The Kano Model of Customer Satisfaction

Developed in 1984 by Dr. Noriaki Kano, the Kano Model provides a non-linear framework mapping the relationship between product execution (ranging from absent to fully implemented) and customer satisfaction (ranging from completely dissatisfied to delighted).

                  Customer Satisfaction
                            ^
                            |       / Attractive / Delighters
                  Delighted |      /  (Unexpected, high delight)
                            |     / 
                            |    /     / One-Dimensional / Performance
                            |   /     /  (Linear: More is better)
                            |  /     /
     Absent                 | /     /                    Fully Implemented
    <-----------------------+------------------------> Execution / Feature Presence
                            |     /     ------------------ Must-Be / Basic
                            |    /      (Taken for granted; absence = rage)
                            |   /
               Dissatisfied |  /
                            |

The Five Kano Categories

1. Must-Be Quality (Basic Requirements / Dissatisfiers):
   • Characteristics that customers take for granted. Customers never explicitly request them because they assume they are inherently present.
   • Behavior: Fulfilling these requirements does not increase satisfaction beyond neutral—the customer merely regards the product as acceptable. However, failing to fulfill them causes severe dissatisfaction and outrage.
   • Technician Examples: Hydraulic fittings that do not leak fluid; a micrometer spindle that moves smoothly; an automotive brake pedal that stops the vehicle.
2. One-Dimensional Quality (Performance Requirements / Satisfiers):
   • Characteristics where customer satisfaction is directly, linearly proportional to the level of execution. The more performance delivered, the happier the customer.
   • Behavior: Customers explicitly discuss and compare these attributes when purchasing.
   • Technician Examples: Battery operating life in hours; tool wear life before needing resharpening; tensile yield strength; fuel economy in miles per gallon.
3. Attractive Quality (Excitement Requirements / Delighters):
   • Innovative, unexpected features that the customer did not anticipate or ask for.
   • Behavior: If absent, there is zero dissatisfaction because the customer had no expectation of receiving them. If present, they generate disproportionate customer excitement, delight, and competitive differentiation.
   • Technician Examples: A digital height gage with built-in Bluetooth that automatically logs calibration offsets; a supplier packaging parts in color-coded, reusable anti-static kitting trays that cut unpacking time by 50%.
4. Indifferent Quality:
   • Features that the customer does not care about whether present or absent. Expanding resources to control indifferent characteristics wastes company capital.
   • Technician Example: High-polish buffing on the internal unexposed surface of an enclosed transmission case.
5. Reverse Quality:
   • Features where higher execution actually produces customer dissatisfaction, or pleases one small segment while alienating the majority.
   • Technician Example: An excessively complex multi-level software password system on a shop CMM that locks out certified inspectors every 15 minutes.

The Dynamic Decay of Kano Categories Over Time

A vital principle tested on quality examinations is that Kano attributes are dynamic and decay over time. Today's Attractive delighter inevitably becomes tomorrow's One-Dimensional performance benchmark, and ultimately degenerates into an expected Must-Be baseline requirement.

• Industrial Example: When carbide inserts with multi-layer PVD wear coatings first appeared, they were an Attractive Delighter. As competitors adopted coatings, tool life became a One-Dimensional Performance comparison. Today, cutting inserts without wear coatings are considered non-viable, making coating an absolute Must-Be requirement.

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Supplier Quality Management (SQM)

In modern supply chains, between 50% and 80% of product value is procured from external sub-tier suppliers. No internal quality system can succeed if it feeds off defective incoming raw materials, uncalibrated hardware, or substandard castings.

The Approved Vendor List (AVL) / Approved Supplier List (ASL)

Under QMS standards (ISO 9001 Clause 8.4, AS9100, IATF 16949), purchasing may only issue purchase orders to organizations on the official Approved Vendor List (AVL). Adding a supplier to the AVL requires:

1. Supplier Self-Assessment / Quality Survey: Comprehensive review of the supplier's QMS, certifications, and financial stability.
2. On-Site Quality Audit: Auditing the vendor's physical plant, machine capabilities, calibration traceability, and nonconformance controls.
3. Sample Part Evaluation / PPAP Submission: Dimensional verification of initial production parts (e.g., First Article Inspection per AS9102 or AIAG Level 3 PPAP submission).

Receiving Inspection Protocols

Incoming receiving inspection serves as the primary technical gatekeeper defending the factory from supplier variation. Organizations deploy three tiers of receiving control:

• 100% Inspection: Required for new unproven vendors, flight-critical components, high-risk medical implants, or suppliers on probation following major quality escapes.
• Acceptance Sampling Plans: Statistical lot-by-lot inspection under ANSI/ASQ Z1.4 (for attribute defect counts) or ANSI/ASQ Z1.9 (for variables dimensional measurements) based on an agreed Acceptable Quality Limit (AQL).
• Dock-to-Stock (Skip-Lot) Certification: Highly mature suppliers with a proven history of zero defects over a sustained period (e.g., 12 consecutive months of zero rejections, $C_{pk} \ge 1.67$, and certified QMS) earn dock-to-stock status. Their shipments bypass receiving inspection entirely and flow directly into inventory, accompanied by a verified Certificate of Analysis (CoA) or Certificate of Conformance (CoC).

Supplier Scorecards and Performance Metrics

Organizations evaluate AVL suppliers continuously using multi-criteria Supplier Scorecards, typically tracking three core pillars:

1. Quality Performance (Typically 40% to 50% Weight):
   • Parts Per Million (PPM) Defect Rate: $\text{PPM} = (\text{Total Defective Parts} / \text{Total Parts Received}) \times 1,000,000$.
   • Lot Acceptance Rate (LAR): $\text{LAR} = (\text{Lots Accepted} / \text{Lots Received}) \times 100%$.
2. Delivery Performance (Typically 30% to 40% Weight):
   • On-Time Delivery (OTD): Percentage of shipments arriving within the acceptable window (e.g., 0 days late / no more than 3 days early).
3. Service & Responsiveness (Typically 10% to 20% Weight):
   • Administrative accuracy of shipping documents and CoCs, responsiveness to corrective action requests, and engineering support.

Supplier Corrective Action Requests (SCAR)

When incoming material fails receiving inspection, causes internal line shutdowns, or exhibits systemic nonconformance, the organization issues a formal Supplier Corrective Action Request (SCAR).

• A SCAR demands a structured problem-solving response—typically using the 8D (Eight Disciplines) methodology:
  • D1: Establish cross-functional team.
  • D2: Describe problem with objective data.
  • D3: Implement immediate containment action (sorting inventory, quarantining in-transit shipments) within 24 hours.
  • D4: Identify true root cause using 5 Whys and Fishbone analysis.
  • D5: Select permanent corrective actions.
  • D6: Implement corrective actions.
  • D7: Prevent recurrence (update supplier PFMEAs, Control Plans, work instructions).
  • D8: Recognize team efforts.

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Technician Role as Internal Customer/Supplier Interface

Quality technicians occupy a pivotal operational position in maintaining customer-supplier integrity:

1. Receiving Inspection Verification: Pulling valid statistical samples, performing mechanical and metallurgical measurements, and cross-referencing supplier Certificates of Conformance (CoC) against blueprint tolerances.
2. Containment of Suspect Material: When receiving inspection detects nonconformance, the technician must immediately execute containment: applying physical Red Quarantine Tags, updating enterprise resource planning (ERP) systems to place inventory on quality hold, and locking material in secure quarantine areas to prevent accidental release.
3. Initiation of Nonconformance Reports (NCR): Logging detailed, objective dimensional and visual data on an NCR to document the exact failure mode, enabling Quality Engineering to initiate an effective SCAR.
4. Feedback Loops to Upstream Operations: When in-process inspection reveals defects, the technician immediately alerts upstream internal suppliers, providing run charts and gage readings to shut down drifting processes before large scrap batches accumulate.

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Technician Inspection Scenarios & Common Exam Traps

Real-World Shop Scenario: Incoming O-Ring Durometer Failure

A quality technician at incoming receiving inspects a lot of 5,000 fluorocarbon (Viton) O-rings intended for high-pressure hydraulic manifolds. The supplier's Certificate of Conformance certifies that the lot meets drawing callout 75 +/- 5 Shore A hardness. The technician pulls a sample of 32 O-rings per ANSI/ASQ Z1.4 and tests them using a calibrated Type A Shore durometer. The sample average hardness is 56 Shore A (unacceptable under-cure condition).

• Compliant Technician Action: Reject the lot, apply red quarantine tags, move the entire shipment to the locked quarantine cage, log an internal Nonconformance Report (NCR), and provide durometer test data to Quality Engineering to issue an immediate SCAR.
• Unacceptable Action: Reworking, accepting on deviation without engineering authority, or relying blindly on the paper CoC when physical testing proves nonconformance.

Common Exam Traps for CQT Candidates

• Exam Trap 1: Misidentifying Must-Be Features in the Kano Model: A common trap is assuming that executing a Must-Be feature exceptionally well creates high customer loyalty. In the Kano Model, basic Must-Be features never delight the customer—they only avoid extreme dissatisfaction.
• Exam Trap 2: Assuming a CoC Replaces Receiving Inspection: A Certificate of Conformance is an administrative document certifying compliance, but it does not replace the necessity for physical receiving verification, especially for new vendors or critical features.
• Exam Trap 3: Issuing a SCAR for Isolated Minor Annoyances: SCARs require formal vendor root cause analysis. They are reserved for systemic failures, safety defects, recurring nonconformances, or large rejected lots—not minor, one-off packaging wrinkles easily rectified via phone call.
• Exam Trap 4: Confusing Internal Customers with Personal Work Preferences: Internal customer requirements are governed by documented product specifications and process flow, not personal operator habits or informal shop agreements.