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A steel seat looks like a simple part, which is exactly why it is often under specified. The dimensional features that make a seat work, meaning face flatness, hole position, and section stiffness, are all produced by a chain of processes in which each step can quietly remove the margin that the previous one created. This guide follows that chain from incoming plate to packed part, and sets out the controls we apply at each stage for seats produced under a quality management system certified to IATF 16949.
Not every seat follows the same route, but the sequence below covers the great majority of the parts we produce. The route is fixed at quotation stage and recorded on the process sheet, so that a repeat order is manufactured the same way as the approved sample.
| Step | Process | Key control |
|---|---|---|
| 1 | Incoming material | Grade certificate, thickness, flatness |
| 2 | Cutting or blanking | Outline dimensions, edge condition |
| 3 | Forming or bending | Angle, radius, springback allowance |
| 4 | Machining and hole making | Hole diameter and position, flatness |
| 5 | Sub assembly welding | Fixture, leg length, distortion |
| 6 | Surface preparation | Cleaning, deburring, pre treatment |
| 7 | Coating | Thickness, adhesion, salt spray |
| 8 | Final inspection and packing | Feature audit, batch record |
Every batch of plate arrives with a mill certificate showing the grade, the heat number, and the mechanical properties. The certificate is checked against the purchase specification and filed against the batch. For carbon structural grades such as Q235 and Q345 this is a documentary check. For alloy grades such as 40Cr and 42CrMo, which are selected for their fatigue behaviour, the grade is additionally verified on the shop floor, because a substituted steel can pass every dimensional check and still fail in service.
Plate thickness is measured at several points across the sheet and compared with the tolerance band. Flatness matters because a bowed sheet carries that bow through forming and shows up later as a distorted mounting face. Material that is outside the agreed band is quarantined rather than sorted into production.
The outline is produced by laser cutting, plasma cutting, or punching, depending on thickness, quantity, and edge quality requirement. Laser cutting gives a clean edge and tight dimensional consistency and suits moderate to high quantity work. Punching is fast for thinner plates and simple outlines but leaves a shear zone that must be deburred. Plasma cutting is economical on thicker plate but produces a heat affected edge that needs preparation before welding.
Every cutting method leaves some edge condition that must be controlled. Dross, sharp corners, and burrs create coating thin spots and stress raisers at weld toes. Corner radii called out on the drawing are there for a reason, and cutting them sharp to save a tool path is a change that should go back through engineering, not be decided at the machine.
Steel does not stay where it is bent. The elastic part of the deformation springs back when the tool releases, so the die must be set to over bend by a calculated amount. Springback grows with higher strength grades, which means a die setting proven on Q235 will not automatically produce the right angle on Q345. Angles are verified with a protractor gauge on the first parts and at defined intervals through the run.
A bend radius that is too tight for the plate thickness causes cracking on the outside of the bend, especially on alloy grades and on material cut with a heat affected edge. The minimum radius is part of the design review, and if the drawing calls for a tighter radius than the material allows, the correction is to change the material or the design rather than to accept a cracked part.
Hole diameter is controlled with plug gauges or an internal micrometer, and hole position is verified on a fixture gauge or coordinate measuring machine against the datum scheme on the drawing. Position capability is the reason the drawing should carry a positional tolerance rather than relying on a general tolerance block: the process can hold a defined band, but only if the band is stated.
After drilling, every hole is deburred on both sides. A burr at the edge of a mounting hole prevents the joint from seating, changes the effective clamp length, and gives coating a place to crack. Deburring is inspected as part of the feature audit, not treated as cosmetic work.
Where the seat is a welded assembly, the fixture defines the product more than the welder does. A rigid fixture with clear locating points, quick clamps, and enough stiffness to hold the part through the cooling cycle is what keeps the mounting face flat and the hole pattern in position. Fixtures are checked periodically for wear at the locating points.
Weld parameters are qualified on the actual material combination and thickness, and the qualified settings are recorded on the process sheet. Leg length is controlled against the drawing and checked visually with a weld gauge. Undercut, porosity, and spatter are treated as rejectable conditions, because each one reduces fatigue life at exactly the location where the load enters the part.
Coating adhesion depends on what is underneath it. Parts are degreased, and where the process requires it, descaled or abrasive cleaned, so that no oil, oxide, or spatter remains before coating begins. Handling after pre treatment is controlled, because a fingerprint on a prepared face becomes a coating defect.
Coating thickness is measured at defined points on a sample from each batch, on faces and inside holes, and the results are recorded against the specified range. Corrosion resistance is verified by neutral salt spray testing to the hours agreed with the customer. Where the seat is a fixed joint face, the drawing may require masking, and the masking plan is part of the process sheet rather than an operator decision.
The table below is the minimum inspection plan we apply to a production seat. The frequency column is the default and can be tightened if the customer requires it or if a capability study shows the process drifting.
| Characteristic | Method | Frequency |
|---|---|---|
| Material grade and certificate | Document review, grade verification | Every batch |
| Thickness | Micrometer, several points | Every batch, first and last part |
| Outline dimensions | Vernier and fixture gauge | First article and hourly |
| Hole diameter | Plug gauge | First article and hourly |
| Hole position | Fixture gauge or coordinate measurement | First article and per shift |
| Mounting face flatness | Surface plate and indicator | First article and per shift |
| Weld leg length and condition | Visual and weld gauge | Every part |
| Coating thickness | Magnetic or eddy current gauge | Per batch, several points |
| Salt spray resistance | Neutral salt spray | Per coating run or per agreed period |
Knowing which defect belongs to which process step shortens the corrective action considerably.
| Defect | Usual source process | Control that prevents it |
|---|---|---|
| Crack at a bend | Forming | Minimum bend radius, correct grade, edge preparation |
| Distorted mounting face | Welding or forming | Fixture rigidity, balanced sequence, springback compensation |
| Oversize or displaced holes | Machining | Tool wear monitoring, positional tolerance on the drawing |
| Burr at hole edge | Machining | Deburring step inspected as a feature |
| Thin or flaking coating | Coating | Pre treatment control, thickness measurement, adhesion test |
| Rust starting at a weld | Coating over spatter | Weld cleaning before pre treatment |
| Wrong steel grade supplied | Incoming material | Grade verification on every alloy batch |
Each batch is identified with a number that links back to the material certificate, the process sheet with its qualified settings, the inspection records, and the coating record. That chain is what allows a field question to be answered with facts rather than recollection. Where a seat forms part of a safety related assembly, the drawing states which records must travel with the shipment, and the packing list references them. Storage is also part of the system: parts are packed so that coated faces do not rub, and boxes are not stacked beyond the level that would bend a thin plate.
The seat selection guide explains how grade and tolerance decisions are made before manufacturing, and the installation guide covers what happens to the part once it reaches the assembly line.
Alloy batches are verified on the shop floor in addition to the documentary check of the mill certificate. This is the control that catches a substituted steel, which is otherwise difficult to detect because a wrong but dimensionally correct grade passes every routine check.
Usually a combination of incoming plate flatness, forming springback, and heat input during welding. The controls are incoming flatness inspection, die settings proven on the actual grade, and a rigid fixture that holds the part through the cooling cycle.
With a magnetic or eddy current gauge on prepared samples, and by destructive sectioning on the first article of a coating run. Inside hole readings matter because a plated pin or bolt has to pass through, so the drawing either allows for the coating or specifies masking.
The batch number, the material certificate with heat number, the process sheet, the dimensional inspection record, and the coating record including salt spray results where applicable. Records for a specific batch can be retrieved on request against that batch number.
Send a 2D or 3D drawing or a physical sample, together with the annual quantity and the application, and our team will propose the process route, the grade, the inspection plan, and the coating specification. See the seat and mount range, review the wider shock absorber parts catalogue, look at the custom manufacturing service, or contact our sales engineers with your requirement.
