2019-05-23
One of the first steps in welding is preparing the mating parts with a bevel. Beveling creates an angle between the edges of a pipe or plate perpendicular to the surface. The bevel creates a path for the pool of metal to fill and reduces the thickness into which the arc must burn. It also ensures visibility in an open arc process and gives the torch tip access to the bottom of the base metal (Figures 1 and 2).
There are many options when it comes to beveling, each with its own benefits, including:
• Waterjet or torch cutting
• Angle or die grinder
• Handheld electric or pneumatic beveling tool, stationary beveling machining or beveling machine that is attached to the piece and progresses on its own, either across a plate edge or around a pipe end
Most fabrication shops will own a cutting torch that can be used for brazing as well as burning a bevel on an edge. Torch cutting is fast, but it leaves a rough edge, and depending on the setup, may not result in the most accurate beveled angle. Torch cutting may also require grinding and finishing to clean up the rough edges before the weld process can begin.
Grinding and finishing are demanding operations that add time and cost. Torch cutting is not the best solution on heat-sensitive metals like stainless steels and can affect the microstructure of the metal. Lastly, torch cutting can release fumes.
Angle grinders are versatile tools for metal removal, cutting and beveling. Grinding is a hard job, and like torch cutting, may not be accurate in holding a specified bevel angle or depth. It can result in high or low spots, as well as overheated or burned spots in the metal, leading to welds of lower quality that may require rework. The grinding process using an angle grinder with a grinding disc, flap disc or fiber disc may also result in contamination of the base metal, which could lead to a weld joint of questionable integrity.
The efficiency of using an angle grinder to bevel decreases as the depth requirement of the bevel increases (Figure 3). Beveling ¼-in plate can be quick; however, the same cannot be said if the operator must bevel a long run of 1-in plate to a full bevel.
On thinner metals, a die grinder and mounted stone or carbide burr can be used, but the effort is even greater than with using an angle grinder and more time-consuming. The use of a die grinder for beveling should be reserved only for small areas inaccessible by other means or on short-run jobs.
Dedicated handheld beveling tools, stationary beveling machining or those that attach to the metal being beveled are available in both electric and pneumatic versions.
Rather than using an abrasive, these typically rely on indexable carbide inserts, which produce chips, reducing dusts and debris. The indexable carbide inserts are mounted on a precisely angled head or into a tool that allows guide plates to be set at the desired bevel angles; the application determines the type. Tools with a router-type base are useful for both external beveling on straight edges as well as shapes, and can be used for beveling of internal shapes. These types of tools require the purchase of a different beveling head for the different desired angles.
Tools with adjustable angled-guide plates save costs since they can set at any desired angle without the need to change out the cutting head. The disadvantage is they are not as versatile on shapes or internal beveling. These types of tools are much more expensive than a plasma torch or a grinder, but they save hours of hard labor, are more precise and will result in better welds that require little rework. The tools also reduce the risk from sparks and flying debris, and are cleaner.
The indexable carbide inserts create chips that drop away. No dust or, in the case of soft metals, combustible dust is produced. Unlike grinding or torch cutting, the tools with indexable carbide inserts create a chip that absorbs the heat, so the base metal is left in an unchanged, cool condition. An additional benefit of the indexable carbide inserts is that there is no contamination of the base metal.
Dedicated beveling tools allow for setting the desired depth of bevel. Depending on the accuracy required, depth is set by turning an index ring and locking in the depth with a set screw. Some tools offer a micrometer-type setting with detent settings as small as 0.004 in, making for extremely precise depth and width of the bevel — this is an advantage over grinding or torch cutting. These types of tools create a consistent bevel angle and depth, ensuring that the weld specification is maintained over the entire length of the joint.
In addition to beveling, some work requires a chamfer or an edge-break specification. The ability to precisely dial in the depth of the beveling tools makes them the ideal tool for this additional application.
The pneumatic tools are typically lighter, but require a compressed air source, making the total cost of setup higher than electric tools. The determination to use pneumatic may rest on whether the shop already has a compressed air source or not. Additionally, recent advances in battery technology have led to the introduction of cordless beveling tools. They have the power for edge breaking, chamfering and beveling to depths of 5⁄32 in for mild steel.
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