Deep-Drawn Stainless Steel Cups: An Application Study in Wall Thinning Control

Control deep drawn stainless steel cup wall thinning by mapping local thickness against a documented starting-sheet reference, then testing the forming hypothesis that the map supports. A cup that looks sound can still require thickness inspection: uneven thickness, cracks and wrinkles are recognized drawing concerns. [4] KEYENCE. The practical goal is to meet the part’s minimum-wall and functional requirements throughout the specified region, while keeping the forming route repeatable.

This application guide develops a hypothetical cup inspection and tryout plan. It shows how to locate a critical region, calculate thickness loss without confusing nominal and actual starting thickness, and choose the next investigation. It does not attempt to select a universal draw ratio or replace a material-specific forming assessment.

Define the cup and the study question

For this example, assume an open cylindrical stainless-steel cup with a nominal outside diameter of 40 mm, a finished height of 45 mm and nominal starting sheet thickness of 1.00 mm. These dimensions identify the imagined component; they do not establish its drawability, blank diameter, number of draws or pressure rating. The material grade and delivery condition remain project decisions requiring supplier documentation.

The question is deliberately narrow: where is the lowest inspected wall thickness, and what evidence would help the team reduce unwanted local thinning? A separate feasibility review should establish the forming route. A separate product assessment should establish the minimum acceptable wall from the service requirements. Neither decision follows from the cup dimensions alone.

Proposed drawing-review inputs are the critical wall regions, dimensional datums, trim condition, surface requirements and the stage at which inspection applies. If a cup will later be flanged, pierced or joined, identify whether the relevant thickness requirement applies before or after that operation. Write the inspection stage into the record so results from different stages are not silently combined.

When arranging a review with SSP’s tooling team, provide the drawing revision and this question together. A useful enquiry asks for a review of the intended evidence and acceptance criteria, without assuming that a photograph or a generic capability statement verifies the proposed cup.

Understand material flow and thinning

In drawing, material feeds inward from the blank through the die and blank-holder region to form the wall. This inward movement distinguishes drawing from stretch forming with a constrained blank. The worldstainless forming chapter illustrates that distinction for ferritic grades. [2] worldstainless. For the cup review, ask whether the proposed operation principally allows draw-in, deliberately stretches a region, or includes an ironing step; Outokumpu lists these as distinct press-forming processes. [1] Outokumpu.

Do not assume the final wall must equal the original sheet everywhere. Outokumpu explicitly discusses thinning in relation to forming mode and stainless family. Tool surfaces and lubrication also matter to formed surface quality. [1] Outokumpu. The proposed investigation therefore treats thickness, material flow and surface condition as related observations, without treating any one of them as a complete explanation.

Material identity must be more specific than “stainless”

BSSA notes both strong work hardening in austenitic stainless steels and differences in drawing behavior within that family arising from composition. [3] BSSA. Austral Wright’s application sheet also cautions against specifying 304DDQ automatically for every difficult drawing enquiry. [6] Austral Wright Metals. Record the actual grade, delivery condition, lot and supplier information before proposing a material substitution.

For this study, request the material certificate and the supplier’s forming guidance, then agree which additional characterization is needed. This proposed sequence follows the logic of published stainless-formability research that first characterizes the sheet and then examines critical component regions and strain paths. [7] Aleksandrović et al.. It is not a claim that tensile elongation alone predicts the cup’s local minimum wall.

Build a repeatable thickness map

The proposed inspection plan assigns each cup a unique ID, marks an angular reference before forming, and preserves its relationship to the sheet’s rolling-direction record. On the cup drawing, define the base, transition and wall measurement zones with coordinates or section locations. Terms such as “near the bottom” are inadequate for comparing later trials.

In the illustrative map below, angular positions are 0°, 90°, 180° and 270° relative to the recorded reference. Five zones give 5 × 4 = 20 tabulated locations per cup. This is a teaching grid, not a recommended sampling density or proof that the smallest thickness anywhere on the component has been found. A real plan should add locations wherever geometry, simulation or observed defects suggest an unexamined risk.

The lowest listed value is 0.82 mm at the base-to-wall transition, at 90°. That observation identifies the next inspection focus in this example. It does not establish that the same location will be critical on another cup, nor that the tool radius caused it. The upper-wall entries exceed both hypothetical starting references used below; retain those signed changes rather than converting them into positive “thinning.”

Choose and qualify an accessible measurement method

Mitutoyo identifies deep-throat micrometers as instruments for sheet-metal thickness measurements. [5] Mitutoyo. KEYENCE discusses access and point-measurement limitations in drawn-part inspection. [4] KEYENCE. Those references do not establish that an arbitrary micrometer can correctly measure this cup’s curved transition.

For the proposed study, ask the inspection team to demonstrate access, contact geometry and repeatability at each named zone. If sectioning is necessary, agree the cutting and preparation method, retain orientation marks and document how thickness is evaluated across the section. If a scanning method is proposed, agree how internal and external surfaces are captured and how the thickness calculation is validated at critical locations. Record inaccessible or unmeasured areas explicitly.

Calculate and interpret thickness loss

For this article, define percentage thickness loss as L = 100 × (t₀ − t) / t₀, where t₀ is the documented initial reference thickness and t is the local finished thickness, expressed in the same units. This is the arithmetic definition used for the example, not a forming-limit criterion.

Assume the drawing calls for nominal 1.00 mm sheet, but a traceable starting-sheet reference for the illustrative material is 0.98 mm. At the hypothetical 0.82 mm location, the nominal-based calculation is 100 × (1.00 − 0.82) / 1.00 = 18.00%. With the assumed actual starting reference, it is 100 × (0.98 − 0.82) / 0.98 = 16.33%, rounded to two decimal places.

The difference at the transition is 1.67 percentage points, rounded. It is a change in the reference basis, not an improvement in the formed cup. The physical example still has a 0.82 mm listed minimum. Keep the two reference bases clearly labelled if both are useful to a customer review.

For a separate acceptance illustration, suppose a product engineer specifies a local minimum of 0.85 mm in that transition region. The listed 0.82 mm would be 0.03 mm below that assumed requirement. Even though 16.33% looks less severe than 18.00%, changing the denominator cannot change that comparison. The 0.85 mm value is an invented drawing requirement, not a stainless-steel standard.

Do not report more confidence than the inputs support. The displayed percentages are arithmetic rounding only. In an actual report, state the measurement method, starting-reference basis and applicable measurement uncertainty or decision rule. Without those records, the example cannot establish a marginal pass, a capable production process or a safe service load.

Turn the map into a diagnostic review

Use the map to form testable questions. BSSA connects blankholding with flange-wrinkle control and highlights the importance of suitable punch and die radii. [3] BSSA. KEYENCE describes cracking associated with excessive constraint in particular drawing operations, and identifies galling with failure of the lubricant film and resulting contact damage. [4] KEYENCE. These mechanisms justify an investigation; they do not identify the cause of the hypothetical 0.82 mm entry.

Use the checklist to decide what to investigate, not to prescribe a universal holder force, die clearance or radius. The tooling/friction discussion in worldstainless supports reviewing the interface, while its recommendations are written in a ferritic context. [2] worldstainless. Keep that scope visible rather than transferring a supplier’s settings to every stainless cup.

Plan controlled trials and retesting

The following is a proposed trial structure. Start with a documented baseline that includes the material lot, blank identification, tool revision, forming sequence, lubricant/application method, approved machine settings and inspection method. Capture intermediate-stage evidence if the team needs to determine when the thin region develops. All changes require the responsible process and tooling team’s review.

For an exploratory example, compare three approved conditions: the baseline, one lubrication-control change and one holder-profile change. Assume four cups per condition, giving 3 × 4 = 12 cups. Applying the illustrative 20-location grid to every cup produces 12 × 20 = 240 thickness entries. These are hypothetical planning quantities, not a statistically justified qualification sample or a claim that any trial has been performed.

Keep the baseline route available for comparison. Record actual settings and reasons for departures rather than only labels such as “trial B.” If a trial requires more than one change, list them and avoid attributing the outcome to a single cause. Record each cup individually; an average can be reported in addition to, but should not replace, the individual minimum-location review proposed here.

Before and after each approved comparison, use the same drawing zones and reference basis. Review the thickness maps alongside wrinkles, surface condition and dimensional results. If the team considers an additional redraw or intermediate annealing, develop a material-specific route review: BSSA discusses staged forming and inter-stage annealing for demanding austenitic drawing, rather than establishing a requirement for every cup. [3] BSSA. This study supplies no furnace recipe or guarantee of a successful redraw.

Create the release record

Proposed release documentation should connect the requirement to the evidence. Retain the approved drawing, material identity, starting-sheet reference, cup IDs, location map, raw values, calculations, inspection method and decision rule. Attach the relevant tool/process revisions and the disposition of each unresolved issue. Published stainless-formability research similarly treats material characterization and component-specific critical regions as connected parts of the investigation. [7] Aleksandrović et al..

For the hypothetical cup, the release discussion remains open: a listed minimum below the invented 0.85 mm requirement would need an approved design or process disposition and fresh evidence. No claimed improvement is available because no comparison trial results have been supplied. The useful output is a reproducible study plan and calculation sheet, not an invented success story.

For the physical tooling, use SSP’s stamping-die product overview to frame the tool enquiry. For the drawing-review, build and trial discussion, use the stamping-die manufacturing service page. Send the cup drawing, material specification, critical-wall zones and acceptance requirements so the proposed scope can be assessed. Request project-specific evidence before relying on any stated capability.

Frequently asked questions

Technical references

Sources were reviewed for this guide on 28 October 2026. Manufacturer and association guidance supports the stated mechanisms within its own scope; it does not validate this hypothetical cup or establish SSP project results.

1. Outokumpu, Forming of stainless steel.
2. worldstainless, Ferritic Stainless Steels, forming chapter.
3. BSSA, Forming techniques: drawing and spinning.
4. KEYENCE, Thickness measurement of drawn products.
5. Mitutoyo, Sheet Metal Micrometer.
6. Austral Wright Metals, Deep Drawing Stainless Steel.
7. Aleksandrović et al., Formability of stainless sheet metals by deep drawing: integral approach.