Quantitative Methods for Analyzing 3D Printing Customer Requirements: Kano Classification, Weighted Scoring, and Priority Ranking

Introduction: Requirements Are Not a Checklist, but a Matter of Priorities

During early-stage discussions for 3D printing projects, the most common challenge is not that customers cannot articulate their needs, but that every statement they make is treated as equally important. A quotation may simultaneously include dimensional accuracy of ±0.05 mm, surface roughness of Ra 1.6, a five-day delivery lead time, a 15% unit-price reduction, and a change of material to titanium alloy. These items sit side by side, with no indication of their relative importance or the cost of giving any of them up. As a result, the engineering team balances them based on its own interpretation, only for the customer to discover at acceptance that the requirement they cared about most was not given priority. The real threshold in requirements management is translating “what the customer said” into “what the customer is willing to pay for and what compromises they can accept.” This translation requires quantitative prioritization tools rather than experience and on-the-spot judgment.

1. Why Requirement Prioritization Loses Focus

There are three typical causes of unfocused requirements. The first is distortion at the expression level: customers describe needs in terms of outcomes—such as “it must fit,” “it must look refined,” or “it must be durable”—while engineering receives them in parameter terms, such as tolerance, roughness, and fatigue life. Without a mapping table between the two, priorities are quietly flattened during conversion. The second is conflict at the stakeholder level: purchasing focuses on unit price, design focuses on accuracy, and assembly focuses on fit. The same requirement can carry entirely different weights across departments, and whoever speaks last temporarily receives the highest priority. The third is the absence of constraints: every requirement exists within a triangular constraint of lead time, cost, and process feasibility. Discussing priorities outside these constraints inevitably causes distortion. Under LPBF, improving surface roughness from Ra 6.3 to Ra 1.6 often requires additional shot peening, vibratory finishing, or even machining. Unit cost may increase by more than 30%, while lead time may extend by two to three days. If the customer’s real priority is receiving an assembly-validation part within three days, the surface-finish requirement should be downgraded to an optional item.

2. The Kano Model: First Classify Requirements into Three Categories

The Kano model qualitatively defines requirements using two dimensions: the horizontal axis represents the degree to which a requirement is fulfilled, while the vertical axis represents customer satisfaction. Requirements falling on three different curves are classified into three categories. Basic requirements are items for which meeting expectations earns no additional credit, while failure results in severe dissatisfaction. Examples include assembly-hole dimensions, tolerances on critical mating surfaces, and consistency between the specified material grade and certification for a 3D-printed part. These requirements must be met unconditionally and should not enter the trade-off pool. Performance requirements are linear items for which better performance produces greater satisfaction, such as surface roughness, delivery lead time, and unit price. Customer satisfaction changes approximately linearly with the degree of fulfillment, making these the main battleground for prioritization. Excitement requirements are items that customers may not request but that create a positive surprise when provided, such as an accompanying CMM inspection report, an assembly and fit-validation video, or a reusable parameter package. These items have relatively low cost but strong perceived value, making them effective differentiation tools. The significance of classification is clear: basic requirements cannot be traded away, performance requirements need scoring and prioritization, and excitement requirements provide low-cost added value.

3. Weighted Scoring Matrix: Scoring Performance Requirements

For requirements in the performance category, use weighted scoring for quantitative prioritization. A five-dimensional model is recommended, with each dimension scored from 1 to 5: customer value (the requirement’s contribution to final assembly or functional performance), implementation difficulty (process complexity and yield risk; higher difficulty receives a lower score), cost sensitivity (the increase in unit cost required to meet the requirement), lead-time impact (the incremental effect on delivery days), and verifiability (whether acceptance can be conducted through quantitative methods; difficult-to-verify items carry higher risk). Weighting factors should be set according to project type. For prototype-validation projects, recommended weights are 0.35 for customer value, 0.30 for lead time, 0.15 for cost, 0.10 for difficulty, and 0.10 for verifiability. For production projects, recommended weights are 0.30 for customer value, 0.30 for cost, 0.20 for verifiability, 0.10 for difficulty, and 0.10 for lead time. Calculate a weighted total score for each requirement and rank them in descending order. Define the top 30% as must-protect items, the middle 50% as optimization items, and the bottom 20% as negotiable items. Scoring must be completed jointly by customer and engineering representatives. Each side should score independently before averaging the results. Items with a scoring difference greater than 1.5 points should be reviewed immediately; this process itself is a high-quality requirements-clarification exercise.

4. From Ranking Results to Technical Specifications

Once prioritization is complete, the results must be formalized in a technical specification; otherwise, they will be diluted in subsequent communication. The specification should include at least four sections. First, it should provide the requirement list and classification results, clearly identifying basic, performance, and excitement requirements. Second, it should define quantitative indicators and acceptance methods for critical characteristics. For example, a Ø8 H7 hole may be inspected using a plug gauge; Ra 3.2 roughness may be assessed by comparison with roughness specimens or by sampling three points with a roughness tester; and material properties may be tested using GB/T tensile specimens from the same furnace batch. Third, it should establish concession-acceptance rules, specifying which indicators may deviate, the permitted deviation range, and the compensation method. Fourth, it should include change-control provisions defining the rescoring and quotation-adjustment mechanism following requirement changes. Once signed by both parties or confirmed by email, the specification becomes the sole basis for first-article inspection and production release. Experience shows that projects with quantified technical specifications typically improve first-article pass rates by 20% to 35%, while significantly reducing rework and communication costs related to disputes.

5. Implementation Checklist

Conduct each requirements review in the following sequence: first, list all original requests without deletion; then classify each item using the Kano model; next, apply five-dimensional weighted scoring and ranking only to performance requirements; then incorporate the ranking results into the technical specification and define acceptance methods; finally, identify two to three low-cost excitement requirements as added-value items. The review meeting should be limited to 60 minutes. Its deliverables should be a prioritization table and a draft specification, rather than meeting minutes. One important reminder: scoring is not a one-time exercise. When the process route changes—for example, from SLS to LPBF—when volume increases from five parts to 200 parts, or when the customer’s mating assembly changes, the weighting factors should be recalculated and the prioritization results updated accordingly.

Conclusion

The core of customer-requirements analysis is not collecting more requirements, but establishing a repeatable prioritization mechanism. Use the Kano model to classify requirements as basic, performance, or excitement requirements; use five-dimensional weighted scoring to establish the priority order for performance requirements; and formalize the results in a technical specification with acceptance methods. In this way, verbal agreement becomes an engineering basis. For additive manufacturing environments involving multiple processes, materials, and post-processing combinations, the value of quantitative prioritization lies not only in reducing disputes, but also in directing limited cost and lead-time budgets toward what customers are genuinely willing to pay for.