Rising demand for sheet metal doors and windows requires manufacturers to fabricate products with minimal scrap and rework to achieve on-time delivery. DFM strategy for sheet metal designs and modern design tools help achieve these goals.
Demand for metal doors and windows is expected to rise at 3.7% per year through 2022, benefitting manufacturers with strong sales over the coming years. The demand forecast though lucrative sounding to any sheet metal doors and windows manufacturer, implies the need for a more competitive work environment.
There is hence an imminent need to improve existing sheet metal design and manufacturing processes by adopting the right design tools with integrated automation to stay competitive.
Let’s take a closer look at these three aspects in detail.
1. Sheet Metal Design Using DFM (Design for Manufacturing) Strategy
One of the major concerns while designing doors and windows is the lack of a designer’s knowledge of sheet metal design. Unlike solids, sheet metal design involves a sound understanding of the physics and manufacturability, as sheet metal parts behave differently in a real-world environment.
Following are some of the key sheet metal design considerations a good designer should know to maintain the design intent and maximize the manufacturing efficiency:
Minimum Bending Radius
Bending radius is critical when considering door and window designs, and it varies depending on the grade of sheet metal used. The frames and plinth of metal doors and windows are an excellent example of section profiles that use bending process.
Insufficient bending radius on these components compromises the flatness of the rabbet on which the door will actually rest. This leads to further inaccuracies in installing and operating the door.
As a rule of thumb, the minimum bending radius for a mild steel sheet metal should be equal to the thickness of the sheet.
Bending radius also depends on the type of brake tool used. The frames for doors and windows usually employ a roll forming method for bending. Bending the sheet to a designer specified bend angle may lead to spring-back effect – a tendency of the sheet metal to retain its original flat form. This happens because the top surface of the sheet undergoes tension and the bottom one is under compression.
This is the reason why the brake operator will overbend to the bending angle, so that the desired bent angle is achieved once the part is released from the pressure. The designer must predict and efficiently account for the springback while developing the designs for doors and windows to avoid change orders later during the manufacturing stage.
Grooves, Ribs, and Holes
While holes are important for fastening the doors and windows using hinges, they also do the job of imparting strength to the formed part. The metal around the area where holes are punched or drilled gets stretched and becomes more tensile, providing better structural rigidity to the sheet. However, the size of the hole and the distance between the two holes are important to consider before punching or drilling them out.
As a thumb rule, the hole diameter should not be less than the sheet thickness, and the distance between two holes must be at least two times the sheet’s thickness. The diameter goes up to two times the thickness of the sheet for stainless steel or alloy material.
Maintaining the hole diameter to stock thickness ratio is important, as punching holes that are smaller than the material thickness causes the stamping forces to spread out instead of going downwards through the material as shown in the figure below.
When this ratio is not followed, the punch often gets stuck into the material, and in many cases, deforms the part altogether. Ultimately, this results in an increase in cost per run and demands more maintenance, delaying the fabrication process further.
However, in case of metal doors, there is a need to punch smaller holes in order to accommodate fastening the locks and hardware items. In such situations, holes are usually produced through drilling or machining process.
Grooves and ribs offer additional strength without adding to the wall thickness and are often used in doors and windows to offer weather tight seal between sections.
Keeping a provision for these elements early during the design stage will reduce the possibility of errors during the punching process.
Notches and Tabs
Sheet metal doors and windows need notches and tabs to make provisions for hinges and locks. But there are a few design parameters to consider when specifying the notch.
The rule of thumb here is that the notch width shouldn’t be narrower than 1.5 times and the length should be maximum 5 times the sheet thickness. The minimum distance between a bend and a notch should be 3 times the material thickness plus the inside bend radius. And, when there are two notches, the space between them should not be less than 2 times the sheet’s thickness.
Minimum Flange Width
Flanges are often useful in reinforcing tops and bottoms of doors with inverted horizontal channels. Reveal flange, for example, is an essential part of the door frame profile which extends from the return and formed parallel to the wall. The minimum height of a bent flange should be proportional to the material thickness, bend radius and length of the bend. The minimum width of a bend relief should at least be equal to the material thickness or 1.50 mm, whichever is greater.
Welding is an ideal solution to join two parts of the material together, but a more important question one needs to ask here is that is it necessary to use welding or fasteners can do the job? Removing the welding process helps reduce manufacturing costs considerably.
For example, making use of knockdown metal door jamb instead of welded ones can reduce the need of welding process to a certain extent. However, these types of jambs are often suitable where the interior walls are finished with drywall or plaster.
Simple modifications in the design such as extending the bracket from the base material instead of attaching it separately can eliminate welds and bring significant cost reductions. However, the designer must also consider the available bending technology at the shop floor before redesigning the part without welds.
2. Sheet Metal Design Tools
While these design tips ensure better efficiency in manufacturing doors and windows, achieving these results require the right technology tools that support the DFM strategy and offer designers the flexibility to quickly design sheet metal parts and generate fabrication drawings for the shop floor.
Popular 3D parametric CAD tools such as SolidWorks and Inventor offer an array of features for the designers to easily develop sheet metal parts with accurate forming and welding details. The tool automatically generates flat patterns with bend compensation, pushing the design to manufacture faster.
3. Integrating Design Automation
What follows after adopting a 3D sheet metal design tool is the ability to automate repetitive design tasks. Design automation is extremely useful while designing custom sheet metal doors and windows that are specific to the building requirements. From the automatic generation of 3D models and flat patterns to cut lists and fabrication drawings, automation shrinks the design cycle to a significant extent.
Tools like DriveWorks for SolidWorks and iLogic for Inventor take automation to the next level by offering the opportunity to develop sales configurator for doors and windows. Such configurators promote guided selling, where a customer simply inputs the sizes and configurations as per his/her requirements and the 3D model along with an estimated cost is displayed upfront.
Hitech helped a leading US-based manufacturer of custom hollow metal doors reduce the design cycle by 70% by implementing design automation and product configurators. The engineering lead time was reduced from a 4-5 days turnaround to same-day engineering and manufacturing.
Open the Door to Greater Efficiency
To meet the growing demand of high-quality sheet metal doors and windows for residential and commercial buildings, the design team must adopt DFM strategies to minimize manufacturing errors. For this, the designer must have a clear understanding of the fab shop and the material used in the process.
With the right CAD tool, implement sheet metal design knowledge and automate repetitive tasks. Open the doors to higher efficiency and ensure better profit margins in a competitive market.