CNC Turning & Precision Grinding · SUS431
SUS431 Precision Parts: 2,000 per Batch, 100% Bore Inspection
For this 2,000-part SUS431 stainless steel batch, OUJI combined rough and finish turning, outsourced centerless grinding and cylindrical grinding of three precision outside diameters under a stated +0.005 mm requirement. Internal burrs could affect the customer’s part function, but OUJI’s existing inspection method could not check inside the bore. OUJI purchased an industrial borescope and introduced 100% internal-bore inspection after deburring. Green heat-number labels kept the parts identified by batch through outside processing.
By Tom Yi, Project Support | Custom Machining & Technical Coordination
Published
At a Glance
- Material
- SUS431 stainless steel
- Process
- CNC turning → centerless grinding (outsourced) → cylindrical grinding → internal deburring → borescope inspection
- Batch size
- 2,000 parts per batch
- Precision OD requirement
- Three ground outside diameters; stated +0.005 mm requirement
- Functional risk
- Internal burrs could affect the customer’s use of the part
- Internal-bore inspection
- 100% inspection using a newly purchased industrial borescope
- Batch control
- Green heat-number labels; outside processing by batch
- Published OD measurement
- 8.003 mm in the photographed micrometer check
Anonymized production drawing
Part geometry, with confidential details removed
The public excerpt retains only the main part outline. Customer and part identifiers, drawing numbers, revisions, dimensions, technical notes and source metadata have been removed. The +0.005 mm value in this case is OUJI’s stated process requirement; acceptance remains feature-specific on the controlled production drawing. Download the anonymized drawing PDF.
01
The Challenge
The difficult feature was inside the part. Burrs in the internal bore could affect the customer’s use of the component, and OUJI’s existing inspection method could not examine that internal area. An acceptable outside diameter would not resolve this functional risk. The order also required control of three precision outside diameters and management of 2,000 parts as a batch while the route crossed an external centerless-grinding operation.
02
OUJI's Approach
OUJI followed a staged route: rough-turn the outside diameter and length; machine the side features and external thread and finish-turn the length; send the identified batch for centerless grinding; cylindrically grind the three precision outside diameters; then remove internal burrs. To make the bore accessible to inspection, OUJI purchased an industrial borescope and used it to inspect every part after internal deburring. Green labels carried material heat numbers, and outside processing was performed by batch.
03
The Result
The process gained a dedicated internal visual check at the point where the original inspection method had a blind spot. Every part in the 2,000-piece batch was subject to borescope inspection after deburring, while heat-number labels supported batch identity through outside processing. The production photographs show the part, tray arrangement, internal inspection and an outside micrometer displaying 8.003 mm. That reading is published as a single photographed dimensional check; 100% refers specifically to the confirmed internal-bore inspection coverage.
Production sequence
From turned blank to inspected internal bore
Dimensional finishing and internal-burr control are separate stages. Centerless grinding was outsourced; the order stayed identified by batch through that handoff.
Rough turning
Rough-machine the outside diameter and length to prepare the part for subsequent operations.
Side features, thread & finish length
Machine the side features and external thread, then finish-turn the length.
Centerless grinding · outsourced
Process the identified parts by batch at the external grinding operation.
Cylindrical grinding · three ODs
Finish the three precision outside diameters under the stated +0.005 mm requirement.
Internal deburring
Remove burrs inside the bore where remaining material could affect the customer’s use of the part.
100% borescope inspection
Inspect the internal bore of every part with the industrial borescope after deburring.
Functional risk / inspection improvement
Make the hidden bore inspectable
The issue was not just removing a burr: OUJI needed to see the internal area to inspect the result. The existing method could not do that, so OUJI purchased an industrial borescope for the job. The probe and screen made the internal bore visible, and inspection covered every part after deburring. This directly addressed the burr risk identified for the customer’s functional use.
2,000 parts / heat-number identification
Keep the batch identified through outside processing
Each production batch contained 2,000 parts. OUJI used green labels carrying material heat numbers to identify the parts, and outside processing was performed by batch. The workshop photograph shows components arranged upright in separate holding boards with the green labels alongside them. Actual heat-number values are masked in the public image.
Photographed dimensional check
Outside-diameter measurement: 8.003 mm
The digital outside micrometer in the production photograph displays 8.003 mm. The reading is reproduced as photographed, alongside the separate process requirement and inspection coverage.
| Control | Requirement or evidence | What it establishes |
|---|---|---|
| Three precision ODs | +0.005 mm stated process requirement | A machining requirement; individual acceptance limits remain on the controlled drawing. |
| Photographed OD check | 8.003 mm | One displayed outside-diameter measurement. |
| Internal bore | 100% borescope inspection after deburring | Every part was included in the internal visual inspection. |
How to read this evidence
The +0.005 mm notation is kept as supplied; it is not rewritten as ±0.005 mm. The public drawing omits nominal dimensions and detailed acceptance limits. This photograph does not establish the other two ground diameters, roundness, runout or batch-wide dimensional conformity. The 100% figure describes internal visual inspection coverage, not a measured yield or zero-defect rate.
Project questions
What machining route was used for this SUS431 batch?
The route was rough turning of the outside diameter and length, side-feature and thread machining with finish turning to length, outsourced centerless grinding, cylindrical grinding of three precision outside diameters, internal deburring and 100% borescope inspection.
Why did OUJI purchase an industrial borescope?
Internal burrs could affect the customer’s use of the part, but the existing inspection method could not inspect inside the bore. OUJI purchased an industrial borescope to make that area visible and inspected every part after deburring.
How were the 2,000 SUS431 parts managed through outside processing?
The batch size was 2,000 parts. Green labels carried material heat numbers, and outside processing was performed by batch. The published photograph retains the label locations and tray arrangement while masking actual heat-number values.
Does the 8.003 mm reading verify all three precision diameters?
The photograph documents one displayed OD measurement. It does not verify all three diameters or the full batch. The case reports the +0.005 mm process requirement separately; the controlled drawing defines acceptance for each feature.
What does 100% inspection mean in this case?
OUJI confirms that every part underwent internal-bore inspection with an industrial borescope after deburring. The claim applies to that internal visual inspection; it does not describe dimensional inspection coverage or a zero-defect rate.
What type of stainless steel is SUS431?
SUS431 belongs to the 431 martensitic stainless steel family. The Atlas Steels grade reference provides general material context. This case does not publish a heat-treatment condition or measured hardness for the parts.
Sources & technical references
- 431 stainless steel grade data sheet — Atlas Steels
General grade reference only. Project material, batch quantity and process details are supplied by OUJI.
- Visual inspection of machined internal holes — Evident Scientific
General explanation of internal-hole inspection access. This is not a statement of the customer’s industry or the brand of borescope used in this project.
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