Are you maximizing your nesting efforts?

Cost reduction seems to be today’s mantra in the manufacturing community. All aspects of a design that can result in cost are scrutinized, and measures are taken to prevent those unwanted and costly elements from making it into final designs.

Material and manufacturing costs are two major elements that influence total product cost. Through thoughtful design, both costs can be controlled or limited at the early design stage itself.

Read more at http://www.thefabricator.com/article/cadcamsoftware/are-you-maximizing-your-nesting-effortsr

Design parts as near rectangle as possible - An assembly example

An electrical cabinet design was originally designed with two parts as shown below.

The assembly contains a T-shaped non-rectangular part. To improve nesting quality, T-shaped part is redesigned into two near rectangular parts. This simple redesign improves material utilization and hence scrap area (Gray shaded) is less and remnant area is more (Pink shaded) as shown below.A saving of 4.583kg is observed for just two assemblies. For customizing nesting application in your CAD modeler, contact tech.sales@geometricglobal.com.

Design your components for maximum material utilization

Material cost governs a major share of product cost in sheet metal products and hence it is advisable to design parts/assemblies for maximum material utilization. All opportunities which can result in improved material utilization have to be analyzed. An interesting case is shown in Fig 1 which gave an utilization of only 39.58% with the original design.To improve the material utilization, the part was redesigned into two pieces as shown in Fig 2, which can be welded together to form the original design. This redesign improved the material utilization to 75.03%. Though material utilization couldn't be improved further due to design limitations, redesign helped to generate 273 pairs of redesigned model compared to 144 numbers of original models from the same sheet size. Welding is an additional process introduced by redesign but it was found that cost of material saving is greater than the additional welding and cutting costs.Visit Nestlib page for more details.

Redesign your components for cost reduction

A work table design modeled as shown below ended up with a nested layout involving lot of scrap.

Original design

Nested layout of the original design

By suitably redesigning the work table as shown below, part utilization increased from 4 part nesting to 6 part nesting in the same sheet and scrap is avoided.

Redesigned Part

Nested layout of the redesigned part

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Methods and Issues in Determining Material Cost for Sheet Metal Parts

Cost of a sheet metal part comprises three major cost components such as material cost, processing cost and overheads. Determining accurate material cost has always been an issue. Theoretically material cost can be calculated as follows:

Material Cost = Area of the flat pattern*thickness*(weight per unit volume)*cost per unit weight.

But this is not a correct estimate as the flat pattern has to be cut from a standard sheet and scrap will be generated while cutting as well as due to the shape of the part. So, various methods are employed by costing professionals to estimate material cost that includes scrap cost. Considering thickness, weight per unit volume and cost per unit weight as constant, part area that accounts for scrap is calculated as follows:

1. Part Area = 1.2 times area of the flat pattern

2. Part Area = Area of the bounding box that encloses the flat pattern

3. The part under consideration is nested in a standard sheet and multiple quantities of same part are nesting. The quantity of the part is selected to fill the entire sheet.
Part Area = A*As/n*A,
Where A - Area of the flat pattern,
As - Area of sheet excluding remnants and
n is the quantity or number of parts nested in the standard sheet.

4. In few other cases, all the parts in an assembly having same sheet thickness are nested in standard sheet with a predetermined lot size.
Part Area = Ai*As/Σ(ni*Ai),
Where Ai - Area of the flat pattern of the ith part,
As - Area of sheet excluding remnants and
ni is the quantity of the ith part nested in the standard sheet.

Methods 3 and 4 are more accurate than methods 1 & 2. If the nesting software is more efficient enough as that of Nestlib, then the nesting software can automatically determine whether method 3 or 4 gives better utilization. Nestlib's optimizer module does this magic. Another important factor is sheet selection as utilization depends on the sheet size used. So, costing will further be more efficient if we can determine the optimal sheet size that gives maximum utilization. This task can also be performed automatically by inventory forecasting module of Nestlib. Even with all these above methods, we can only get a near accurate cost because the nested layouts at design stage involve only the particular part/assembly. Manufacturing might use a different nested layout involving other parts/assemblies. For a contract manufacturer, the nested layouts might even involve parts from different clients. But for costing, nested layouts at the design stage form a baseline for cost estimation and dictates a minimum utilization to be achieved during manufacturing.
i.e. if an utilization of 75% is achieved in design and an utilization of 85% is achieved in manufacturing, then it is acceptable. But if an utilization of 70% is achieved in manufacturing due to other assemblies, then manufacturing should use the nested layout given by design.

Automatic Remnant Determination

Nowadays business is highly competitive and manufacturing firms are looking for ways and means to reduce cost at each and every stage. Reducing scrap is an important activity, which can result in considerable cost saving. Given a set of parts, It is always not possible to use the entire sheet. For example, in a sheet size of 48"x72", the parts may occupy only a portion of the sheet as shown in the figure below.

Nested Layout

The usable remaining sheet, gray shaded area in the nested layout is called remnant sheet and can be used for nesting parts in the next manufacturing run. From nested layouts, determining such remnant sheets is generally a manual activity. Nestlib provides options to determine remnant sheets automatically. Various remnant shapes like rectangular remnant, stepped remnant, true shape remnant can be determined.

Rectangular Remnant

Stepped Remnant


True Shape Remnant

Automatic sheet selection for nesting

Given a set of parts, selecting a right sheet size manually is always a menace to the manufacturing engineers. Because, material utilization for the same set of parts on different sheet sizes are not same. Further, there are other challenges faced by manufacturing engineers such as

1. Sheet selection from standard sheets
2. Sheet selection from standard sheets as well as Remnant sheets
3. Combinatorial sheet selection
4. Unique sheet selection

Given all such challenges, manual sheet selection would prove laborious and inefficient in selecting the optimal sheet. Very often manufacturing engineers settle for sheets with suboptimal material utilization, which increases scrap and thereby increases manufacturing cost. With the present day need for cost cutting, these are potential problems that can be easily addressed by automating the sheet selection process. Nestlib's inventory forecasting module provides such an automated sheet selection option.

1. Sheet selection from standard sheets
Standard sheets sizes such as 48"x72", 60"x72", 72"x72", 72"x144", 96"x144", etc., are commercially available. Manufacturing engineers have to choose a sheet with maximum material utilization from these standard sheets, which requires lot of iterations. Nestlib can automatically choose the right sheet for a given set of parts.

2. Sheet selection from standard sheets as well as Remnant sheets
In certain manufacturing runs, the nested layout for a given set of parts may not consume the whole sheet. In such cases, the remaining sheet, which is called as remnant sheet is generally used for nesting the next lot of parts. Sheet selection task can get more complicated when remnant sheets from previous manufacturing runs are also to be analyzed for utilization. For a given set of parts, Nestlib can choose the right combination of standard sheets as well as Remnant sheets. Nestlib can also give remnant sheets automatically for each nested layout, which can be used for nesting in consequent manufacturing runs.

3. Combinatorial sheet selection
As multiple standard sheet sizes are available, a combination of various sheet sizes for a given set of parts may lead to maximum material utilization. For example,it might turnout profitable to select 2 numbers of 48"x72" sheets and one 72"x144" sheet for a given set of parts. Nestlib provides such a combinatorial sheet selection which automatically selects a combination of various sheet sizes with maximum material utilization as the decision criteria. Nestlib includes remnant sheets also in such combinatorial selection.

4. Unique sheet selection
Sometimes it may be necessary to nest in same sheet sizes. For manufacturing large lot sizes, identical layout in same sized sheets will render use of same die, which will reduce setup time and tooling cost. The problem is to identify the unique sheet size from among the standard sheet sizes. For example if a set of parts need 50 numbers of 48"x72" sheets and 30 numbers of 72"x144" sheets, it may be profitable to nest all the parts in either 48"x72" sheets or 72"x144" sheets depending on maximum material utilization. Nestlib offers such unique sheet selection as well, where nesting is performed on same sheet size for all the parts and the unique sheet size that gives maximum material utilization is selected.