How to optimise part nesting on a tube and control the end remnant ART-194

Distinguish purchased length from usable length

The nominal tube length in the order is not the length available for parts. Some of it may be occupied by an uneven end, a locating allowance, the initial cut zone, chuck contact, regripping, final separation and a guaranteed process tail. Actual stock lengths also have a tolerance. If CAM treats every six-metre tube as exactly identical, the final part may not fit on a shorter workpiece.

Usable length is determined for the specific configuration and operating mode. It may change with diameter, cross-section, weight, chuck arrangement, loading type and required unloading method. That is why the catalogue minimum remnant cannot simply be subtracted from the nominal length and the problem considered solved.

For planning, maintain at least four quantities:

1. the ordered or expected length; 2. the measured actual stock length; 3. the technologically available length for the current programme; 4. the actual remnant after completion.

The differences show where loss occurs: purchasing tolerance, end preparation, the nesting algorithm, machine setup or record-keeping.

Which constraints nesting must recognise

The algorithm must not optimise only the sum of geometric lengths. Each part has process parameters: kerf width, common or separate cuts, safe distances between contours, microjoints, cutting order, support for the separated portion and the cutting head's working zone. Profiles add angular orientation, while welded tubes add the permissible seam position.

Typical constraints include:

• minimum distance between adjacent parts;
• chuck and support exclusion zones;
• length required for regripping;
• feasibility of a common end cut;
• part direction relative to the seam or surface;
• maximum length and weight for the selected unloading channel;
• sequence of short and long parts;
• transition time between different processes;
• stability of the remaining stock after large cutouts;
• the rule for retaining a reusable remnant.

If even one constraint is entered by the operator at the machine, the offline result is not the final nest. Define which data reside in CAD/CAM, which come from the machine and who is responsible for keeping them current.

Calculate material utilisation from accepted parts

A ratio based only on the geometric sum can look excellent even when some parts are damaged during unloading or require rework. A practical metric must connect consumed material to the number of accepted products.

For a batch, it is useful to break the length down into components:

| Component | Example content | Management question | |---|---|---| | Length of accepted parts | Nominal part lengths under the approved rule | What useful yield was achieved? | | Process gaps | Cuts, clearances, starting and finishing sections | Do they match the process? | | Planned tail | Unavoidable clamping or regripping zone | Has it been validated for the configuration? | | Unplanned scrap | Defects, programme errors, incorrect length | Who owns the cause? | | Reusable remnant | A length with identification and conditions for reuse | Has it been returned to inventory? |

This breakdown matters more than a single attractive utilisation figure. It shows what programming can reduce, what depends on the mechanics and what arises from data discipline.

Part sequence affects the process

For specific LT6 and LTX machines, BLM GROUP describes dynamic compaction, which determines the sequence of parts along the tube to reduce end scrap and facilitate unloading. This confirms that nesting is more than packing lengths together. However, the capabilities and criteria of the particular algorithm must be checked on real programmes.

Placing long parts at the beginning or end changes workpiece behaviour. A series of large windows may weaken the tube early. Short parts may need a different receiving channel. Parts using different gases, focus settings or contour types create additional transitions. Sometimes grouping by process reduces time more than minimising the tail does.

Compare at least three strategies: maximum material utilisation, minimum cycle time and a balanced option incorporating quality rules. The software must show not just an image but quantitative consequences: required stock quantity, expected scrap, time, number of regrips and unloading route.

Mixed orders offer the greatest potential

When each order is nested separately, a remnant occurs at the end of every batch. Combining compatible parts from different orders can improve material utilisation but creates new risks: mixed-up products, missed deadlines, and differing certificate and surface requirements.

Only parts with compatible attributes may be combined. Matching external dimensions is insufficient. Material, standard, wall thickness, surface condition, batch or heat number, traceability requirements and process route must be identical or explicitly permitted equivalents. If a certificate is tied to a customer or order, mixed nesting must preserve that link.

For each mixed programme, create an output map identifying which item, quantity and container belong to each order. Material savings must not become sorting and searching costs.

A reusable remnant is more than a piece of metal

A length must be identified before it can return to inventory. It needs a profile, material, thickness, actual length, batch, surface condition, date, storage location and end condition. Without these data, a remnant often sits beside the machine before being scrapped or used without traceability.

Set the minimum return-to-stock length by tube group rather than using one number for all tubes. A shorter length of an expensive special profile may be worth retaining than of a common carbon-steel tube. At the same time, the piece must be long enough for safe loading and clamping. If the machine cannot use it without non-standard intervention, the accounting “inventory” has no production value.

Mark the remnant before its context is lost. If it leaves the machine without a label, recovering the heat number later may be impossible. Do not rely on a marker-pen inscription as the sole system where certified traceability is required.

Actual length must close the planning loop

After the batch, the system must compare calculation and actual results. Measure the initial stock, accepted part quantity, scrap and reusable remnant. If the discrepancy is consistently large, do not immediately blame nesting. The cause may be incorrect kerf width, an additional end cut, manual trimming, tube slippage, unrecorded scrap or measurement error.

A useful weekly report contains:

• planned and actual consumption by profile;
• planned and actual tail length;
• numbers of remnants created and reused;
• remnant write-offs by cause;
• material consumed by unaccepted parts;
• programmes with the largest deviations;
• savings from mixed nests.

These data are intended to improve rules, not punish the operator. If a metric encourages hiding short remnants or defects, record quality will deteriorate.

A common cut is not always free

Combining the ends of two parts into one cut saves length and time but changes separation conditions. Check whether one edge is suitable for both parts, how heat is dissipated, what retains the product and where the final portion goes. A common cut may be unacceptable for parts with different tolerances or end requirements.

Do not enable it globally. Create permitted families and validate them with a series. Assess the geometry of both parts, burrs, squareness, length and damage during separation. If manual deburring is required, the saving of a few millimetres may disappear.

A short tail can increase risk

The drive to minimise remnants sometimes pushes the process into an unstable clamping zone. The final part may be cut after regripping, close to the chuck or with little supported length. Accuracy, collisions, scrap evacuation and chuck condition must be validated separately.

The mechanically achievable tail is covered by ART-175. For nesting, the key point is different: the algorithm must not use the smallest stated value universally for every profile. Store the validated minimum in the rules library by material, cross-section, weight, clamping arrangement and final-part type.

Test the software using your own data

Use order history rather than a demonstration set: identical series parts, a mixed production day, expensive material, short products, long frames and a batch with different deadlines. Give different systems or strategies identical input data for each set.

Check whether it is possible to fix order priority, prohibit batch mixing, specify a reusable remnant, reuse it, block an unsafe seam position, see why a case was rejected and export the plan. ART-188 discusses software testing on your own assemblies more broadly; here the focus is only on material and remnants.

FAT: prove the result, not the image

The control test must start with measured tubes and finish with a material-balance reconciliation. Ask the supplier to generate a nest without manually changing the original drawings. Record the software version, rules, calculation time and all manual interventions.

After cutting, count accepted parts, scrap and the remnant. Check that each part reached the correct container and that the reusable length received an identifier. Repeat the test with a shorter workpiece within the purchasing tolerance. The system must either rebuild the plan or clearly warn of insufficient length, rather than start the last part without enough material.

How to choose the target metric

A single material-utilisation percentage for the entire workshop is insufficient. Compare within homogeneous groups: material, profile, batch size, complexity and process constraints. For management, use a set of metrics: accepted-part yield, actual tail length, proportion of remnants reused, minutes per tonne or metre, rework and on-time order completion.

The optimal nest is the one that produces the best validated result for the current priority, not the densest image. It must be executable on the machine, preserve quality, maintain traceability and close with an actual material balance.

The order queue and nesting are one problem

The densest local nest can worsen overall workshop performance if an urgent part waits for a compatible order. Nesting must therefore receive priority, due date, permitted combinations and maximum waiting time. The planner must see both the material saving from postponement and the delivery risk it creates.

A combining horizon can be set for each group. Common profiles allow a short wait for mixed nesting, special material is planned against a specific certificate, and emergency orders run separately. The rule must be transparent; a manual decision to “wait a little longer in case another part appears” makes delivery unpredictable.

Assess a full day or week, not a single workpiece. A nest leaving an additional tail on the first tube may reduce changeovers and deliver better overall yield. Use the same order set for verification and compare tube count, accepted parts, time, overdue orders and remnants created.

Account for kerf width and the actual end

Even in a one-dimensional model, length is not merely the sum of nominal part lengths. Kerf width, entry strategy, initial end trimming and finished-length tolerance affect every cycle. If CAM uses the wrong kerf value or omits an additional end cut, the calculated tail will systematically differ from the actual one.

Check the length of several parts from different positions along the workpiece. An accumulating deviation may come from the length model or slippage. A deviation that is consistent for each part may come from end compensation or the measurement criterion. Corrections must be made by the data owner, not hidden in a manual allowance in every programme.

Managing the remnant library

A remnant must undergo the same checks as a new tube. On return to inventory, it receives an identifier, measured length, material, batch, profile, end condition and location. Before replanning, the system checks minimum loading length, clamping availability and certificate compliance.

It is useful to distinguish statuses: usable without preparation, requires end trimming, reserved, under inspection and unusable. Otherwise, the planner sees a theoretical metre of metal that the operator cannot safely use. Accumulate write-off reasons: lost identification, corrosion, damage, insufficient length or lack of demand. These statistics show whether the retention policy truly makes economic sense.

Verification after a CAM version change

A software update may change the nesting algorithm, default distances, common-cut rules or time estimates. Before switching production, run the control set without cutting and compare the result with the approved version. A significant change in stock count or tail length requires an explanation.

Retain input data, version, parameters and report so that the result can be reproduced. If the operator manually moves parts, those changes must also be visible. Automatic optimisation is useful only to the extent that the company understands its constraints and can verify the actual balance.

Who owns each parameter

Assign responsibility before launch. Purchasing owns stock format and length tolerance; the designer owns geometry and permitted common cuts; the process engineer owns gaps and sequence; the planner owns priority and mixing; the warehouse owns remnant identification; and the operator owns execution and actual results. If one person can change every field unnoticed, reproducing the plan becomes difficult.

Each deviation must have a reason code: short stock, additional end trimming, scrap, manual change, unloading failure or lost remnant. This allows the source to be corrected instead of continually increasing the safety tail. Review the largest causes monthly and update only validated rules.

Monitor unfinished programmes after an emergency stop separately: the actual position, parts already cut and available remnant must be reconciled again before resuming, otherwise the digital balance will lose its connection to the tube.

CTA. Send L-SEL your tube list, batch quantities, part drawings and remnant tracking rules. We will help formulate a benchmark task for comparing nesting, cycle time and material utilisation.

Limits of application

Vendor functions do not guarantee the best result on every part set. Clamping parameters, minimum tail, common-cut feasibility, traceability rules and economic priorities must be validated for the specific configuration and production operation.

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