Quoting stamped and sheet-metal parts

Why quoting is the bottleneck

An RFQ for pressed parts arrives as a pack: scanned drawings, STEP models for some parts, an assembly drawing with its bill of materials, a spreadsheet of annual volumes, sometimes a photo of the current part. The price has to be built from all of it.

For every part, an estimator answers the same questions. What is the material, and what does it cost this month? How much steel must be bought to make one? Which operations does the drawing require, in what order, on which press? What goes out for plating or heat treatment? Each answer depends on the one before, and most are worked out again for every part.

Slow answers lose work, because buyers move on with the quotes they have. Inconsistent answers lose margin. Two estimators given the same bracket can arrive at different gross weights, routes and prices, and the quotes that win are disproportionately the low ones. An inconsistent process wins its underpriced jobs and loses its correctly priced ones.

The knowledge that makes a quote right lives with people: which die fits which press, what the plater charges, which customer expects which breakdown. It leaves when they do.

Anatomy of a quote

A quote for a pressed part is a sum of lines, each with its own basis. Names vary between shops; the structure is stable.

• Material. Gross weight × the price per kilogram for the exact grade, thickness and form, less a credit for offcut sold as scrap. It is often the largest single line.
• Process. Each operation priced from its machine and time, whether a press stage, tapping, welding, deburring or inspection. Presses are priced per machine hour × cycle time, or per stroke and tonne of rating.
• Bought-out parts. Catalogue items such as weld nuts, fasteners, bushes and clips, at unit price × quantity.
• Outside processes. Work that leaves the shop and comes back, often called job work: plating, coating, heat treatment, priced the way the supplier charges.
• Policy lines. Overheads, a rejection allowance, packing, freight and profit, each a percentage of named lines or a fixed amount per piece, set once in the shop’s costing policy.

Tooling sits apart. Dies, fixtures and gauges are a one-time cost, usually quoted as a lump sum that the customer pays for and owns; some shops amortise it into the piece price. It belongs on the quote either way, because nested layouts and progressive tools trade higher tooling for a lower piece price.

Assemblies add structure. A bracket with two weld nuts is a parent whose children are the pressed plate, with its own material and operations, and the bought nuts. Welding, the finish on the assembly drawing and joint tests belong to the parent, because they happen after joining. Plating charged on the child and again on the assembly is the same work quoted twice.

Gross weight decides the material line

Three terms carry the material line. Net weight is the mass of the finished part, usually printed on the drawing. The flat blank is the part unfolded: its outline before bending, with every hole cut. Gross weight is the steel bought to make one part: the flat blank plus its share of everything cut away around it.

Blanks are cut from strip, slit from coil or sheared from sheet. The strip layout is the arrangement of blanks on that strip. The die needs an edge margin between the blanks and the strip edge, and a web between neighbouring blanks, commonly about 2 × and 1.5 × the thickness, with a floor of a few millimetres on thin sheet. The pitch is the distance the strip advances per stroke. Utilisation is the share of bought steel that ends up in the part; the rest is offcut, sold as scrap for a scrap credit.

The layout is a real decision. A blank can run one-up, every blank the same way round; rotated 90°, which changes the strip width and the pitch; or nested, with alternate blanks turned head to tail so their outlines interlock. Bends in hard or high-strength steel should run across the rolling direction, burr side and appearance faces fix which way up a blank sits, and two parts per stroke need a two-cavity die. Strips sheared from sheet also lose material at strip ends and sheet edges.

Take the bracket from the worked example below: 3 mm steel, with a flat blank shaped as a trapezoid that tapers from 140 mm to 80 mm over 104.8 mm. Its three candidate layouts differ by up to 81 g of steel per part.

This is why a reviewer’s first question is “why this gross weight?” A drawn layout answers it in seconds; a bounding box plus an allowance leaves the reviewer to redo the work. Every candidate should show its working, with what it saves per piece and adds in tooling.

A worked example

The numbers here are an invented, internally consistent example. The part is support bracket SB-2150 for Kestrel Automotive, at 120,000 a year. The drawing specifies cold-rolled close-annealed (CRCA) steel, grade DC04, 3.0 mm thick; one 90° bend at 3 mm inside radius, with outside legs of 60 and 50 mm; two Ø10.5 mm holes in the base and one in the upright; zinc plating; and a net weight of 265 g.

Flat blank. Unfolding a bend shortens the outside legs by a bend deduction. With the neutral axis at 0.44 of the thickness (the K-factor), the bend allowance is π/2 × (3 + 0.44 × 3) = 6.8 mm and the deduction 2 × (3 + 3) − 6.8 = 5.2 mm, so the flat length is 60 + 50 − 5.2 = 104.8 mm. The flat area, less the three holes, weighs 265.4 g at 3.0 mm and 7.85 g/cm³, within 0.2% of the drawing. The unfold holds.

Layout. DC04 is a deep-drawing grade that bends comfortably along the rolling direction, so the nested layout is open. Each blank advances by its mean width of 110 mm plus the web, which is measured square to edges leaning 16° from the cross direction: 4.5 ÷ cos 16° = 4.7 mm along the strip.

Route and price. A two-cavity compound die blanks the outline and pierces the base holes. The part is bent, the upright hole is pierced on the bent part (the next section explains why), and the parts are deburred, zinc plated by a supplier, inspected and packed. The shop runs 63, 100, 160 and 250 t presses; its machine-hour rates, including the operator, are $60 for the 63 t and $85 for the 160 t. Its costing policy adds a 2% rejection allowance, 8% overheads on material and process, fixed packing and freight, and 10% profit.

Tooling is quoted separately: $14,000 for the two-cavity compound die, $4,000 for the bending die, $3,500 for the pierce die and $1,500 for a checking gauge, $23,000 in all. A one-up compound die would cost about $8,000. Nesting adds $6,000 of tooling, saves $0.076 of material per piece, about $9,100 a year, and repays the difference in about eight months.

Material is the largest line at $0.366, a third of the price, followed by plating and the two hand-fed press stages. That ranking shows where review time pays.

Operations, presses and tooling

The route follows the drawing: stock preparation, blanking and piercing, forming, sizing such as restrike or coining, secondary work, finishing and inspection. Stages combine wherever one die can do the work: blank and pierce in a compound die, bends that share an axis and direction in one forming die.

The drawing can change that order. A hole whose edge sits closer to a bend than about 2.5 × thickness + inside radius distorts as the flange forms, so it is pierced afterwards. On the example bracket that zone is 2.5 × 3 + 3 = 10.5 mm, and the upright’s hole sits 8 mm from the bend, toleranced from the base. Holes in opposite flanges that must share an axis go further: a cam tool, driving its punches sideways, pierces both after bending in one stroke, locating on the formed part, so they line up on the finished bracket.

Press force. For cutting, force = cut length × thickness × shear strength. The example’s compound die cuts two outlines and four holes per stroke, 1,008 mm in all. At a conservative 300 MPa for DC04, that is 1,008 × 3.0 × 300 = 907,200 N, or 92.5 tonnes-force. Bending is usually an order of magnitude lighter, about 2 t here. Coining is the exception: pressing a zone flat takes about three times the tensile strength over the contact area, and it often decides the press.

Tonnage is a press’s rated force. The required rating is the calculated force × a safety factor for blunt tools and material at the top of its strength range; 1.5 is a common default. Here 92.5 × 1.5 = 139 t, so the smallest adequate press is the 160 t, loaded to 58%. Larger presses cost more per hour, so the choice is the smallest one whose rating and bed fit the die.

Tandem or progressive. A tandem route gives each stage its own die, with the part moved between presses by hand or transfer; the tools are cheaper, which suits low and medium volumes, thick material and short programmes. A progressive tool is one die with several stations: coil advances one pitch per stroke, every station works on every stroke, and a finished part drops off the end. It costs more, needs a press sized for the sum of its stations, and runs far faster. The example needs 500 parts a day over 240 working days, at most 500 strokes a day on any press: comfortably tandem. As a rough guide, a progressive tool deserves a price once a hand-fed press would pass 5,000 to 6,000 strokes a day, weighed as per-piece saving × annual volume against the extra tooling. Here it would also need a carrier web, giving back part of the nesting gain.

Work that leaves the shop

Plating, coating, heat treatment and shot blasting usually go to specialists. On the quote they are outside operations, kept apart from bought-out parts and priced as the supplier charges: platers and heat treaters per kilogram, often with a minimum lot charge, painters and powder coaters often per unit area. Transport and any handling uplift are lines of their own.

Per-kilogram pricing needs the processed mass: the example’s plating is 0.265 kg × $0.95/kg = $0.252. Per-area pricing needs the treated surface, which the flat blank gives directly: both faces, 2 × 11,268 mm², plus 537 mm of cut edge × 3.0 mm, about 24,150 mm² or 2.4 dm². A finish on an assembly drawing is applied after welding and priced once, on the parent.

Sometimes a drawing asks for a process the shop has never offered: a zinc-nickel finish, a salt-spray test, induction hardening. That requirement belongs in the quote as a heads-up: planned as an outside operation, priced at a stated rate marked as an assumption, with a request for a supplier’s price. The shop decides whether to find a partner, and the customer still gets a complete quote on time.

Where estimates go wrong

The costly errors are ordinary ones. On the example bracket:

• A stale material price. If steel has moved from $1.20 to $1.32/kg since the price list was updated, material rises by $0.038 per piece, half of what nesting saved. The price for the exact grade, form and date deserves as much care as the layout.
• A missing finish. Leaving out the zinc plating under-quotes the bracket by $0.282 once its rejection allowance and profit are counted, about a quarter of the price.
• A missing operation. Piercing the upright hole flat saves $0.100 per piece and a $3,500 die on paper, and produces holes that miss their position tolerance.
• An optimistic gross weight. Pricing the nested yield while planning a one-up die under-quotes material by $0.076 per piece, about $9,100 a year.
• A policy line applied twice. Packing charged as an operation and again as a policy line, or profit charged on a child part and again on its assembly. Each line looks reasonable on its own.

Each is caught the same way: by recording where every number came from. A gross weight that points to a drawn layout, a price that points to a dated price list and an operation that points to the callout that forced it can each be checked in seconds by someone who did not build the quote. A number without a source can only be trusted or redone.

How CAS approaches it

CAS produces a complete first quote with its working attached. An agent reads every file in the RFQ pack: drawings and scans page by page, including title blocks, notes and BOM rows, then STEP models, DXF flat patterns and volume spreadsheets. It builds the part tree: which parts are made, which are bought and which operations belong to an assembly.

For each made part it unfolds the flat blank, checks it against the drawing’s net weight and proposes two to four strip layouts. The server computes each gross weight from the layout, thickness and density, so the layout the estimator sees is the one that was priced. The agent plans operations on the shop’s own machines, rates, safety factor and costing policy, choosing the smallest press that can run each die.

Every value carries its source: a region of a drawing, a model measurement, a calculation, the shop’s price list, a user’s answer or a stated assumption. Decisions, assumptions, missing information, heads-ups and inconsistencies between documents arrive as one short list, ranked by their effect on price. Open questions come with a suggested answer and the price of each option, and the agent completes the quote while they wait.

The estimator keeps the judgement. Any number can be edited directly or changed in chat (“run the blanking on the 250 t press”, “steel is $1.32/kg this month”), and the quote re-prices with the change recorded. Lasting corrections become company notes the agent reads on every future project. The quote exports in the shop’s own sheet format, with the margin kept internal. See Quotation for the product.