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Views: 101 Author: 深圳市博森威电气有限公司 Publish Time: 2026-09-03 Origin: BSUMWELL
If you are an electrical wholesaler or EPC procurement professional considering custom housings (perforations, CNC machining, non-standard sizes), this article will help you clarify:
Why are customized products more prone to quality problems than standard products?
How to re-verify the IP rating after drilling and CNC machining?
What are the differences in the quality control process for customized orders, from prototyping to mass production?
How can the buyer ensure the consistency of quality in customized orders?
This article was written by the BSUMWELL technical team. We are a manufacturer specializing in waterproof electrical enclosures, with products covering three major material series: PC/ABS plastic, stainless steel, and aluminum enclosures, with protection levels ranging from IP67 to IP68. We also support OEM/ODM customization.
Many buyers have a misconception: if standard products are made well, customized products can be just as good.
The truth is quite the opposite. The quality control of customized products is far more difficult than that of standard products.
The reason is simple:
Dimension | Standard products | Customized products |
Process Flow | Fixed | Each order is different. |
Testing standards | Mature and stable | Need to be redefined |
worker skill | Highly skilled | Adapting to new requirements every time |
Risk points | Known and controllable | Unknown and constantly changing |
The biggest risk of customization is not "whether it can be made", but "whether it can be verified after it is made".
Standard products have fixed IP ratings, dimensional tolerances, and appearance standards, with established testing procedures. However, the testing standards for customized products need to be redefined based on specific opening locations, dimensional requirements, and special structures—a step that many factories skip.
Trap 1: Not retesting IP rating after drilling.
The standard enclosure undergoes IP testing before leaving the factory. However, after opening the hole, the sealing structure is altered—the fit between the cable connector and the opening edge, as well as the compression path of the sealing ring, may change. Without retesting, the IP rating becomes meaningless.
Trap 2: Burrs and edges are not removed after CNC machining.
After CNC drilling, tiny burrs will be generated at the edge of the hole. These burrs can cut the sealing ring of the cable connector, causing waterproofing failure. Many factories consider "drilling the hole and calling it a day" without smoothing the edges.
Trap 3: Non-standard dimensions use the tolerance standards of standard products.
The outer shell dimensions of standard products are fixed, and the mold precision has been verified. The dimensional tolerances of non-standard customization (especially small-batch CNC machining) need to be reset—using the tolerance standards of standard products may not be sufficient.
A：Yes. Openings disrupt the original sealing structure of the enclosure—the fit between the cable connector and the opening edge, as well as the compression path of the sealing ring, may change. For our custom orders, after opening and CNC machining, we re-perform the IP waterproof test 100% to ensure that the customized enclosure still meets the IP67/IP68 rating.
A：No, they are different. The quality control standards for standard products are mature and stable, but the quality control standards for non-standard customized products may vary from batch to batch. Our customized orders undergo three stages of verification before mass production: DFM review, full-size inspection of T1 samples, and small-batch trial production. Only after the stability is confirmed will they enter formal mass production.
A：Custom-made casings involve additional design verification and prototyping stages compared to standard products—DFM review (2-3 days), T1 sample production and testing (5-10 days), and small-batch trial production and verification (3-5 days). It is recommended to allow sufficient time for prototyping and only start mass production after confirmation.
Customized quality control doesn't begin when "production starts," but rather when "design is confirmed."
The core value of DFM (Design for Manufacturability) review is:Before production, we need to solve the problems of "can it be made?" and "how to make it well?"
The content of the DFM review:
Opening location assessment: Is the opening located where the structural strength allows? Will it affect the sealing performance?
Tolerance setting: Are the tolerances on the customer's drawings reasonable? Can CNC machining achieve them?
Sealing structure confirmed: Is the sealing path complete after the hole is drilled? Is a special sealing ring required?
Assembly feasibility: For custom-sized components, are the assembly paths for internal parts clear?
The value of DFM review: Intercept risks during the design phase before starting the mold/CNC program—instead of discovering they "cannot be installed" or "cannot be sealed" after the mold is made.
Real-world examples: A European customer recently ordered a batch of stainless steel junction boxes, requesting three M20 cable openings on the bottom of the housing. Our DFM review revealed that the openings on the customer's drawings were only 3mm from the edge of the sealing groove—far below our recommended minimum edge distance (8mm). If the original drawings were followed, the sealing ring would not fully cover the opening area, inevitably compromising the IP rating. We suggested adjusting the opening positions and provided the customer with revised drawings. Only after customer confirmation did we begin CNC machining. The final delivered products successfully passed the IP68 test, and the customer commented, "Luckily, you discovered this problem beforehand."
Our custom orders undergo DFM review by our engineering team before mold making or CNC machining. The review report will clearly identify risk points and recommend solutions; production will only begin after customer confirmation. Contact us for DFM audit consultation]
Quality control for customized products begins with a clear and complete set of technical drawings and a Bill of Materials (BOM).
Technical drawings must include:
Standard three-view drawing of the housing (including all critical dimensions and tolerances)
Detailed specifications of the opening location, size, and shape.
The surface finish of the opening edges must meet certain requirements (this directly affects sealing performance).
Partial sectional view of special structure
The Bill of Materials (BOM) must include:
Shell material and specifications
Matching cable gland specifications
Sealing ring material and size
Fastener material and specifications
All other accessories
A complete set of technical drawings and a Bill of Materials (BOM) serves as the "construction blueprint" for customized quality control. The factory constructs according to the drawings, and the quality control inspects according to the drawings—the clearer the drawings, the more accurate the quality control.
T1 sample is the one completed after the mold or CNC program is finished. First batch of samples.
This is the most important inspection point for customized quality control because:
All the problems will be exposed for the first time on the T1 sample.
The earlier a problem is detected by T1, the lower the cost of fixing it.
If T1 fails, it will proceed directly to the next round of optimization and will not enter mass production.
Inspection contents of sample T1:
Full-size inspection: Refer to the technical drawings and measure all critical dimensions item by item (according to ISO 2768 standard).
Assembly verification: Assemble all components and confirm the installation path and space.
Seal verification: IP waterproof testing (at least IP66/IP67) verifies the customized sealing performance.
Appearance verification: Surface quality, edge smoothness of openings, coating integrity.
Only when all T1 samples pass 100% of the inspection items can they enter the small-batch trial production stage.
The fact that the T1 sample passed does not mean that there will be no problem with mass production.
The T1 sample was "meticulously crafted"—engineers oversaw the entire process, and every detail was carefully considered. However, under mass production conditions, workers cannot possibly devote the same level of attention to every single product.
The value of small-batch trial production: verifying the consistency of quality under mass production conditions.
Key points for small-batch trial production:
Production conditions are consistent with mass production: Using the same equipment, the same process parameters, and the same operators.
Sampling inspection: Sampling inspection is conducted according to AQL standards to assess the batch quality level.
Process capability assessment: Does the Cpk (process capability index) for the critical dimensions meet the target? (Target value Cpk ≥ 1.33).
Customer confirmation: Only after the trial production batch is confirmed by the customer can it enter formal mass production.
Our customized orders strictly follow a four-stage process: "T1 Sample → Small Batch Trial Production → Customer Confirmation → Formal Mass Production".Each stage has clearly defined quality control points and release standards.
Drilling holes is the most common processing method for customized orders, but it is also the process with the highest quality control risk.
Three key points for opening quality control:
Step 1: Position accuracy verification
Deviations in the hole position directly affect the installation and sealing performance of the cable connector. If the hole deviation exceeds the tolerance, the cable connector may not be aligned, or the sealing ring may not be evenly compressed.
Inspection method: Use a coordinate measuring machine (CMM) to verify the opening position.
Step 2: Edge smoothness inspection
Burrs and sharp edges on the opening can cut the sealing ring of a cable connector. Even if the hole is perfectly aligned, a single burr can disqualify it from being rated IP.
Inspection method: visual inspection + tactile inspection (slide your fingertip along the edge to confirm there are no burrs or sharp edges).
Step 3: Dimensional accuracy confirmation
The opening diameter must match the cable connector specifications. If it is too large, the seal will not be tight; if it is too small, installation will be impossible.
Inspection method: Use a go/no-go gauge or calipers to measure the diameter of the opening.
CNC machining is often used for custom requirements such as non-standard size shells, special openings, and threaded holes.
Key points for quality control in CNC machining:
Quality control dimensions | Detection methods | Quantitative Standards | Frequently Asked Questions |
Dimensional accuracy | Coordinate Measuring Machine (CMM) | Tolerance ±0.05mm (according to ISO 2768-m grade) | Dimensional deviations caused assembly failure |
Surface roughness | Surface roughness tester | Ra≤1.6μm (sealing surface) | Excessively rough surface affects sealing and appearance. |
Thread quality | Thread plug and plug gauge | Go gauge passes, stop gauge stops | Damaged threads prevent fasteners from tightening. |
Burr control | Visual and tactile inspection | The edges are free of sharp edges and burrs (according to ISO 13715 standard). | Unremoved burrs affect assembly and safety. |
Secondary sealing verification after CNC machining:
CNC machining alters the original structure of the housing—specifically by adding openings or changing the wall thickness. Any structural changes require a complete retest of the IP waterproof rating.
Our CNC custom orders undergo a 100% secondary IP waterproof test after machining is completed. — Ensure customization does not compromise the protection rating. [Learn about our OEM/ODM customization services]
Customized orders often come with sealing systems that are not "standard configurations"—the opening locations change, the cable connector models change, and the compression path of the sealing rings changes.
Three core checks for sealing system quality control:
Sealing ring installation verification
After the hole was drilled, did the installation position and compression path of the sealing ring change? Can the sealing ring completely cover the drilled area?
Testing method: After installation, check the position of the sealing ring to confirm that there is no twisting or offset.
Cable joint seal verification
Is the cable connector tightly fitted to the opening? Is the sealing ring evenly compressed?
Inspection method: Use a torque wrench to confirm the tightening torque + visually inspect the compression state of the sealing ring.
Overall IP Test
After all custom processing is completed. The entire IP waterproof test must be redone. —It's not just about measuring "the location of the opening," but rather the overall sealing integrity of the entire casing.
All our custom orders undergo a 100% IP waterproof test upon completion of all processing. — Ensure that the customized enclosure still meets the IP67/IP68 rating.
The final inspection of customized orders cannot use the same template as for standard products. Each customized order should have its own unique final inspection checklist.
Outer shell (standard item)
[ ] The material and specifications meet the BOM requirements.
[ ] The appearance is free of scratches, burrs, and color differences.
Custom openings (customization item)
[ ] The opening position meets the requirements of the technical drawings.
[ ] The opening size meets the requirements of the technical drawings.
[ ] The edges of the opening are smooth, without burrs or sharp edges.
CNC machining (custom items)
[ ] Dimensional accuracy meets the requirements of the technical drawings.
[ ] The thread quality meets the standard.
[ ] Surface roughness meets requirements
Sealing and IP testing (custom item)
[ ] The sealing ring is installed correctly and is not twisted.
[ ] The overall IP waterproof test after customization passed (IP67/IP68).
Supporting components (standard items + customized items)
[ ] All components are of the correct specifications (Cable Gland, screws, seals, etc.)
[ ] Complete quantity of accessories
Special customer requirements (customization items)
[ ] The silkscreen/laser engraving content is accurate.
[ ] Packaging requirements have been met
Each of our custom orders comes with its own final inspection checklist. The checklist is customized item by item based on the client's technical drawings and BOM to ensure that "everything that needs to be inspected is inspected".
For large-volume or high-requirement customized orders, we support third-party testing and on-site inspection by the customer.
Third-party testing:
Third-party organizations such as SGS and TÜV conduct on-site testing at the factory.
Sampling inspection shall be conducted in accordance with the AQL standards required by the customer.
Issue an independent test report
Customer on-site inspection:
The customer sent personnel to the factory for on-site inspection.
Acceptance is carried out item by item according to the client's internal standards.
Shipment after inspection and approval
We support third-party SGS testing and on-site customer inspection. This provides double assurance for the quality of customized orders.
Many buyers like to check "how clean the workshop is" and "how much equipment there is" when they inspect a factory. These are certainly important, but what truly determines the quality of customized products is "process" and "system".
Ask these 5 questions during your next factory inspection:
Do you have a Design Factor (DFM) review process for custom orders?
If the other party says, "We'll do it if the client gives us the drawings"—that's very risky.
If the other party says, "We have an engineering team to review drawings and provide DFM reports"—that's a plus.
"How did you handle the problem found in sample T1?"
If the other party says, "We'll fix it if there's a problem," it shows a lack of systematic process.
If the other party says, "We have a T1 review meeting, we record issues and track closures"—that's a plus.
"After drilling and CNC machining, do you retest the IP rating?"
If the other party says, "No need, drilling a hole won't affect the seal"—this is a warning sign.
If the other party says "100% retest" - that's a plus.
"Is there a specific final inspection checklist for customized orders?"
If the other party says, "A list of standard products will suffice"—high risk.
If the other party says, "We create a customized checklist for every order"—that's a plus.
Do you support third-party testing or customer inspection?
If the other party says, "I don't support it, it's too much trouble"—high risk.
If the other party says, "We support you; we have a well-established cooperation process"—that's a plus.
[Contact us for details on quality control for customized orders.]
In addition to the five questions above, there are three more details you must ask:
① "How to deal with the burrs after drilling?"
If the other party answers, "The worker will file it down"—that's the problem. The correct approach should be "setting the deburring path in the CNC program" or "using a dedicated deburring tool + inspection standards".
② What standard was used for the customized IP testing?
If the other party answers "IEC 60529"—correct. If the other party answers "our own standard" or "let's do a random check"—dangerous.
③ "Have there been any problems with previous custom orders? How were they handled?"
A factory that is willing to share its failures and explain how it improved is more trustworthy than one that simply says, "We never have problems."
Customized products are far more difficult to control than standard products. — The process and testing standards are different for each order.
Quality planning during the design phase is crucial. — DFM review and technical drawing confirmation determine half of the quality.
Three-level validation during the prototyping stage — T1 Sample → Small Batch Trial Production → Customer Confirmation: Each step is indispensable.
The IP rating must be remeasured after drilling and CNC machining. — After structural changes, the seal integrity must be re-verified.
Custom orders require a unique final inspection checklist. — The template for standard products is not applicable to customized products.
(Previous article: Understand the whole process quality control system? Please read the first article in this series, "...") From raw materials to finished products: The end-to-end quality control system of an electrical enclosure manufacturing plant (IQC→IPQC→FQC→OQC)》)
(Next article preview: Mastered customized quality control? Next, learn how to audit the quality control capabilities of an electrical enclosure factory—15 factory audit checklists. Please read the third article in this series, "How to Audit the Quality Control of an Electrical Enclosure Factory—15 Checklists for the Purchasing Party.")
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